Expandable lordotic intervertebral fusion cage

ABSTRACT

An intervertebral fusion cage includes first and second endplate members, first and second ramp members, and an actuator. The first and second ramp members and first and second endplate members have complementary ramp surfaces that engage to expand the height of the fusion cage and to impart a lordotic profile to the fusion cage.

TECHNICAL FIELD

The present invention relates to an expandable intervertebral implant.

BACKGROUND

The human spine is comprised of a series of vertebral bodies separated by intervertebral discs. The natural intervertebral disc contains a jelly-like nucleus pulposus surrounded by a fibrous annulus fibrosus. Under an axial load, the nucleus pulposus compresses and radially transfers that load to the annulus fibrosus. The laminated nature of the annulus fibrosus provides it with a high tensile strength and so allows it to expand radially in response to this transferred load.

In a healthy intervertebral disc, cells within the nucleus pulposus produce an extracellular matrix (ECM) containing a high percentage of proteoglycans. These proteoglycans contain sulfated functional groups that retain water, thereby providing the nucleus pulposus within its cushioning qualities. These nucleus pulposus cells may also secrete small amounts of cytokines such as interleukin-1.beta. and TNF-.alpha. as well as matrix metalloproteinases (“MMPs”). These cytokines and MMPs help regulate the metabolism of the nucleus pulposus cells.

In some instances of degenerative disc disease (DDD), gradual degeneration of the intervertebral disc is caused by mechanical instabilities in other portions of the spine. In these instances, increased loads and pressures on the nucleus pulposus cause the cells within the disc (or invading macrophages) to emit larger than normal amounts of the above-mentioned cytokines. In other instances of DDD, genetic factors or apoptosis can also cause the cells within the nucleus pulposus to emit toxic amounts of these cytokines and MMPs. In some instances, the pumping action of the disc may malfunction (due to, for example, a decrease in the proteoglycan concentration within the nucleus pulposus), thereby retarding the flow of nutrients into the disc as well as the flow of waste products out of the disc. This reduced capacity to eliminate waste may result in the accumulation of high levels of proinflammatory cytokines and/or MMPs that may cause nerve irritation and pain.

As DDD progresses, toxic levels of the cytokines and MMPs present in the nucleus pulposus begin to degrade the extracellular matrix. In particular, the MMPs (as mediated by the cytokines) begin cleaving the water-retaining portions of the proteoglycans, thereby reducing their water-retaining capabilities. This degradation leads to a less flexible nucleus pulposus, and so changes the loading pattern within the disc, thereby possibly causing delamination of the annulus fibrosis. These changes cause more mechanical instability, thereby causing the cells to emit even more cytokines, typically thereby upregulating MMPs. As this destructive cascade continues and DDD further progresses, the disc begins to bulge (“a herniated disc”), and then ultimately ruptures, causing the nucleus pulposus to contact the spinal cord and produce pain.

One proposed method of managing these problems is to remove the problematic disc and replace it with a device that restores disc height and allows for bone growth therethrough and between the adjacent vertebrae. These devices are commonly called fusion devices, or “interbody fusion devices”. Current spinal fusion procedures include transforaminal lumbar interbody fusion (TLIF), posterior lumbar interbody fusion (PLIF), anterior to psoas (ATP), extraforaminal lumbar interbody fusion (ELIF), and lateral lumbar interbody fusion (LLIF) procedures. While interbody fusion devices are known in the art, there continues to be a need for minimally invasive devices that stabilize the spinal segment and create an optimum space for spinal fusion.

SUMMARY

In accordance with one aspect, an expandable intervertebral fusion cage is configured for insertion in an intervertebral space defined between a superior vertebral body and an inferior vertebral body. The fusion cage can include a cage body and an actuator. The cage body can include upper and lower endplate members, and proximal and distal wedge members. The upper endplate member can define an upper bone contacting surface configured to abut the inferior vertebral body, and can include at least one proximal upper ramp surface and at least one distal upper ramp surface. The lower endplate member can define a lower bone contacting surface configured to abut the superior vertebral body, wherein the upper and lower bone contacting surfaces are opposite each other along a transverse direction. The proximal wedge member can have at least one upper ramp surface that abuts the at least one proximal upper ramp surface of the upper endplate member. The distal wedge member can have at least one upper ramp surface that abuts the at least one distal upper ramp surface of the upper endplate member. The proximal and distal wedge members can be opposite each other along a longitudinal direction that is perpendicular to the transverse direction. The cage body can define a first side and a second side opposite the first side along a lateral direction that is perpendicular to each of the longitudinal direction and the transverse direction. The actuator can have an actuator shaft that is coupled to the proximal and distal wedge members, such that movement of the actuator in a first direction causes the proximal and distal wedge members to move in an expansion direction whereby (i) the at least one upper ramp surface of the proximal wedge member rides along the at least one proximal upper ramp surface of the upper endplate member in surface contact with the at least one proximal upper ramp surface of the upper endplate member, and (ii) the at least one upper ramp surface of the distal wedge member rides along the at least one distal upper ramp surface of the upper endplate member in surface contact with the at least one distal upper ramp surface of the upper endplate member, thereby causing an entirety of the upper endplate member to move away from the lower endplate member. Movement of the proximal and distal wedge members in the expansion direction causes the upper endplate member at the second side of the fusion cage to move away from the lower endplate at a greater rate than the upper endplate member at the first side of the fusion cage moves away from the lower endplate member.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of illustrative embodiments of an intervertebral fusion cage of the present application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the expandable fusion cage of the present application, there is shown in the drawings illustrative embodiments. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown. In the drawings:

FIG. 1A is a perspective view of an intervertebral fusion cage disposed in an intervertebral space in a contracted position;

FIG. 1B is a perspective view of the fusion cage illustrated in FIG. 1A, but shown expanded from the contracted position to an expanded position;

FIG. 2 is an exploded perspective view of the fusion cage illustrated in FIG. 1A, including upper and lower endplate members, first and second wedge members, an actuator shaft, and at a pair of stop members;

FIG. 3A is a perspective view of the lower endplate member illustrated in FIG. 2 ;

FIG. 3B is another perspective view of the lower endplate member illustrated in FIG. 3A;

FIG. 4A is a perspective view of the upper endplate member illustrated in FIG. 2 ;

FIG. 4B is another perspective view of the upper endplate member illustrated in FIG. 3A;

FIG. 5A is a perspective view of the first wedge member illustrated in FIG. 2 ;

FIG. 5B is a side elevation view of the first wedge member illustrated in FIG. 5A;

FIG. 5C is another side elevation view of the first wedge member illustrated in FIG. 5A;

FIG. 6A is a perspective view of the second wedge member illustrated in FIG. 2 ;

FIG. 6B is a side elevation view of the first wedge member illustrated in FIG. 6A;

FIG. 6C is another side elevation view of the first wedge member illustrated in FIG. 6A;

FIG. 7A is a perspective view of the fusion cage illustrated in FIG. 1A, shown in the contracted position;

FIG. 7B is a perspective view of the fusion cage illustrated in FIG. 1B, shown in the expanded position;

FIG. 7C is an end elevation view of the fusion cage in the expanded position as illustrated in FIG. 7B;

FIG. 8A is a side elevation view of a first side of the fusion cage illustrated in FIG. 7A, shown in the contracted position;

FIG. 8B is a side elevation view of the first side of the fusion cage illustrated in FIG. 8A, but shown in the expanded position;

FIG. 9A is a side elevation view of a second side of the fusion cage illustrated in FIG. 7A, shown in the contracted position;

FIG. 9B is a side elevation view of the second side of the fusion cage illustrated in FIG. 9A, but shown in the expanded position;

FIG. 10A is a cross-sectional view of the fusion cage illustrated in FIG. 9A, showing the actuator in a fully seated position when the fusion cage is in the contracted position;

FIG. 10B is a cross-sectional view of the fusion cage illustrated in FIG. 10A, showing the actuator in an elevated position when the fusion cage is in the expanded position;

FIG. 11A is a sectional side elevation view of the fusion cage of FIG. 10A shown in the contracted position; and

FIG. 11B is a sectional side elevation view of the fusion cage of FIG. 11A shown in the expanded position with the stop members engaged to prevent further expansion of the fusion cage.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Certain terminology is used in the following description for convenience only and is not limiting. The “lower” and “upper” designate directions in the drawings to which reference is made. The words, “anterior”, “posterior”, “superior,” “inferior,” “medial,” “lateral,” and related words and/or phrases are used to designate various positions and orientations in the human body, but also applies to the fusion cage when disposed outside the human body. The terminology includes the above-listed words, derivatives thereof and words of similar import.

Unless otherwise indicated, the terms “substantially,” “generally,” and “approximately” along with derivatives thereof and words of similar import as used herein with respect to dimensions, values, shapes, directions, and other parameters can include the stated dimensions, values, shapes, directions, and other parameters and up to plus or minus 10% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 9% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 8% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 7% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 6% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 5% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 4% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 3% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 2% of the stated dimensions, values, shapes, directions, and other parameters, such as up to plus or minus 1% of the stated dimensions, values, shapes, directions, and other parameters.

Method steps and apparatus described or referenced herein will sometimes be described in singular form for clarity. However, it should be appreciated that as used herein, the singular term “a” or “the” with respect to an apparatus or method step can include the plural apparatus or method steps. Conversely, the plural term as used herein with respect to apparatus or method steps can include the singular “a” or “the.” Thus, it should be appreciated that the use herein of the singular term “a” or “the” and the use herein of the plural term can equally apply to “at least one” unless otherwise indicated.

Referring to FIG. 1A, an intervertebral implant or fusion cage 20 can be inserted into an intervertebral space 22 in an initial or contracted position. The intervertebral space 22 can be disposed anywhere along the spine as desired, including at the lumbar region, thoracic region, or cervical region of the spine. The intervertebral space 22 can be defined by a first or superior vertebral body 24 and a second or inferior vertebral body 26. The superior vertebral body 24 defines a superior vertebral surface 40, and the adjacent inferior vertebral body 26 defines an inferior vertebral surface 42. The superior vertebral surface 40 and the inferior vertebral surface 42 can face each other so as to define the intervertebral space 22. The vertebral bodies 24 and 26 can be anatomically adjacent vertebral bodies, or can remain after a vertebral body has been removed from a location between the vertebral bodies 24 and 26, for instance during a corpectomy procedure. The intervertebral space 22 of FIG. 1A is illustrated after a discectomy has been performed, whereby the disc material has been removed or at least partially removed to prepare the intervertebral space 22 to receive the fusion cage 20.

The fusion cage 20 can be inserted into the intervertebral space 22 along any suitable approach as desired, such as a lateral approach during a lateral lumbar interbody fusion (LLIF) procedure. The fusion cage 20 thus defines a distal end 32 which can also define a leading end of the fusion cage 20 with respect to insertion into the intervertebral space 22, and a proximal end 34 that can also define a trailing end of the fusion cage 20 that is opposite the distal end 32. As used herein, the term “proximal” and derivatives thereof refer to a direction from the distal end 32 toward the proximal end 34. As used herein, the term “distal” and derivatives thereof refer to a direction from the proximal end 34 toward the distal end 32. The proximal and distal ends 34 can be opposite each other along a longitudinal direction L, which can be oriented substantially along the medial-lateral direction when the fusion cage 20 is disposed in the intervertebral space 22. The fusion cage 20 is designed and configured to be inserted into an intervertebral space in a direction from the trailing end 34 toward the insertion end 32, also referred to herein as an insertion direction. The insertion direction can also be oriented along the longitudinal direction L.

Referring now to FIG. 1B, once the fusion cage 20 has been inserted into the intervertebral space 22, the fusion cage 20 can be expanded from the first or contracted position to a second or expanded position. The fusion cage 20 achieves a height in the expanded position that is greater than the height of the fusion cage 20 in the contracted position. Further, the fusion cage 20 can angulate to achieve a lordotic profile as it expands from the contracted position to the expanded position. The fusion cage 20 can therefore be said to undergo lordotic expansion as it iterates from the contracted position to the expanded position. As a result, the fusion cage 20 can achieve height restoration of the intervertebral space 22 while supporting the vertebral bodies 24 and 26 in alignment with each other consistent with the natural curvature of the spine.

Referring also to FIG. 2 , the expandable fusion cage 20 defines a cage body 21 having an upper endplate member 36 and a lower endplate member 38 opposite the upper endplate member along a transverse direction T that is perpendicular to the longitudinal direction L. The cage body 21, and thus each of the upper and lower endplate members 36 and 38 defines a first side 23 and a second side 25 opposite the first side 23 along a lateral direction A that is perpendicular to each of the longitudinal direction L and the transverse direction T. A first lateral direction is thus established from the second side 25 toward the first side 23. A second lateral direction opposite the first lateral direction is established from the first side 23 toward the second side. The endplate members 36 can be formed of polyether ether ketone (PEEK) or any other suitable biocompatible polymeric material. Alternatively, the upper and lower endplate members 36 and 38 can be made of any suitable biocompatible metal such as a titanium-aluminum-niobium (TAN) alloy. It should be appreciated that the any suitable alternative material can be used to form the endplate members 36 and 38 as desired.

The upper endplate member 36 defines an upper bone contacting surface 28 that is configured to abut or grip the superior vertebral surface 40. The lower endplate member 38 defines a lower bone contacting surface 30 that is configured to abut or grip the inferior vertebral surface 42. The bone contacting surfaces 28 and 30 can be opposite each other along the transverse direction T. Each of the upper and lower bone contacting surfaces 28 and 30 can be convex or partially convex, for instance, one portion of the surface is convex while another portion can be substantially planar. Alternatively, each of the upper and lower bone contacting surfaces 28 and 30 can be substantially planar along their respective entireties. While the upper and lower bone contacting surfaces 28 and 30 are shown as smooth in FIG. 2 , it is recognized that the upper and lower endplate members 36 and 38 can include any suitable texture that extends from the upper and lower bone contacting surfaces 28 and 30, such as teeth, spikes, ridges, cones, barbs, indentations, or knurls, which are configured to grip the superior and inferior vertebral bodies 24 and 26, respectively, to resist migration of the fusion cage 20 in the intervertebral space 22.

The upper endplate member 36 further defines at least one first or proximal upper ramp surface 37 and at least one second or distal upper ramp surface 39. Similarly, the lower endplate member 38 defines at least one first or proximal lower ramp surface 41 and at least one second or distal lower ramp surface 43. The at least one first upper ramp surface 37 can be generally aligned with the at least one first lower ramp surface 41 along the transverse direction T. Similarly, the at least one second upper ramp surface 39 can be generally aligned with the at least one second lower ramp surface 43 along the transverse direction T. The at least one first upper ramp surface 37 can extend generally toward the upper bone contacting surface 28 as it extends in the proximal direction. The at least one second upper ramp surface 39 can extend generally toward the upper bone contacting surface 28 as it extends in the distal direction. The at least one first lower ramp surface 41 can extend generally toward the lower bone contacting surface 30 as it extends in the proximal direction. The at least one second lower ramp surface 43 can extend generally toward the lower bone contacting surface 30 as it extends in the distal direction.

The fusion cage 20 is initially inserted into the intervertebral space 22 in the contracted position, the fusion cage 20 defines a first height (see FIG. 8A) from the upper endplate surface 28 to the lower endplate surface 30 along the transverse direction T. The first height can be less than the distance between the superior vertebral surface 40 and the inferior vertebral surface 42 along the transverse direction T. Thus, in some examples, the fusion cage 20 can be inserted into the intervertebral space 22 without distracting the superior and inferior vertebral bodies 24 and 26, respectively, away from each other.

The cage body 21, and thus the fusion cage 20, further includes at least one wedge member disposed between the upper and lower endplate members 36 and 38. The at least one wedge member has at least one ramp surface, and is configured to move in an expansion direction, which causes the at least one ramp surface to ride along a corresponding at least one ramp surface of at least one of the upper endplate member 36 and the lower endplate member 38 to move away from the other of the upper endplate member 36 and the lower endplate member 38, and to angulate with respect to the other of the upper endplate member 36 and the lower endplate member 38 along a direction that is angularly offset (such as perpendicular) with respect to each of the transverse direction T and the expansion direction.

The at least one wedge member can include a first or proximal wedge member 44 and a second or distal wedge member 46 opposite the first wedge member 44 along the longitudinal direction L. The wedge members 44 and 46 can be made of any suitable biocompatible polymer such as PEEK, or any suitable metal or metal alloy such as titanium, TAN, stainless steel, or the like. When the fusion cage 20 is in the contracted position, the first wedge member 44 can be disposed at the trailing end 34 of the fusion cage 20, and the second wedge member 46 can be disposed at the leading end 32 of the fusion cage 20. The first and second wedge members 44 and 46 are configured to move from an initial position in an expansion direction that urges at least one or both of the upper and lower endplate members 36 and 38 to move away from the other of the upper and lower endplate members 36 and 38 along the transverse direction T, thereby expanding the cage body 21 and thus the fusion cage 20 from the contracted position to the expanded position. When the wedge members 44 and 46 are in the initial position, the fusion cage 20 is in the contraction position.

In particular, the first wedge member 44 can include at least one upper proximal ramp surface 45 and at least one lower proximal ramp surface 47. The second wedge member 46 can similarly include at least one upper distal ramp surface 49 and at least one lower distal ramp surface 51. The at least one upper ramp surface 45 and the at least one lower ramp surface 47 of the first wedge member 44 can be configured to ride along the at least one first upper ramp surface 37 of the upper endplate member 36 and the at least one first lower ramp surface 41 of the lower endplate member 38, respectively. In this regard, the first wedge member 44 can urge either or both of the upper and lower endplate members 36 and 38 away from the other of the upper and lower endplate members 36 and 38 during movement of the first wedge member 44 in the expansion direction. Similarly, the at least one upper ramp surface 49 and the at least one lower ramp surface 51 of the second wedge member 46 can be configured to ride along the at least one second upper ramp surface 39 of the upper endplate member 36 and the at least one second lower ramp surface 43 of the lower endplate member 38, respectively. In this regard, the second wedge member 46 can urge either or both of the upper and lower endplate members 36 and 38 away from the other of the upper and lower endplate members 36 and 38 during movement of the second wedge member 46 in the expansion direction.

The ramp surfaces of the upper and lower endplate members 36 and 38 and the ramp surfaces of the first and second wedge members 44 and 46 can be nonplanar. In particular, as described in more detail below, the ramp surfaces of the upper and lower endplate members 36 and 38 and the ramp surfaces of the first and second wedge members 44 and 46 can be shaped such that the second side 25 of the fusion cage 20 expands at a greater rate of expansion than the first side 23 of the fusion cage 20. That is, movement of the first and second wedge members 44 and 46 in the expansion direction causes the upper endplate member 36 at the second side 25 of the fusion cage 20 to move away from the lower endplate 38 along the transverse direction T at a greater rate than the upper endplate member 36 at the first side 23 of the fusion cage 20 moves away from the lower endplate member 38. Further, movement of the first and second wedge members 44 and 46 in the expansion direction causes the lower endplate member 38 at the second side 25 of the fusion cage 20 to move away from the upper endplate 36 along the transverse direction T at a greater rate than the lower endplate member 38 at the first side 23 of the fusion cage 20 moves away from the lower endplate member 38. Accordingly, the second side 25 of the fusion cage can achieve a greater height than the first side 23 along the transverse direction T when the implant is in the expanded position. Thus, either or both of the bone contacting surfaces 28 and 30 can be sloped toward the other of the bone contacting surfaces 28 and 30 as they extend in the second lateral direction. As a result, the fusion cage 20 can define a lordotic profile (or kyphotic profile if the fusion cage 20 is a cervical fusion cage) to assist in restoring the natural curvature of the spine when the fusion cage 20 is implanted and in the expanded position.

The first and second wedge members 44 and 46 are also configured to move in a contraction direction that urges or permits at least one or both of the upper and lower endplate members 36 and 38 to move toward the other of the upper and lower endplate members 36 and 38 along the transverse direction T, thereby iterating the cage body 21 and thus the fusion cage 20 from the contracted position to the expanded position. As will be described in more detail below, the first wedge member 44 can be configured to couple to one or more instruments configured to insert the fusion cage 20 into the intervertebral space and/or expand the fusion cage 20 from the contracted position to the expanded position and/or inject bone graft material into the fusion cage 20. In particular, the first wedge member 44 can also receive bone graft material that promotes fusion of the fusion cage 20 to the superior and inferior vertebral bodies 24 and 26, respectively.

The fusion cage 20 further includes an actuator 48 that is coupled to each of the first and second wedge members 44 and 46, and is configured to cause the first and second wedge members 44 and 46 to move selectively in a first or expansion direction that causes the fusion cage 20 to iterate from the contracted position to the expanded position, and a second or contraction direction that causes the fusion cage 20 to iterate from the expanded position to the contracted position. The expansion direction and the contraction direction can be oriented opposite each other along the longitudinal direction L.

The actuator 48 can include an actuator shaft 50 that extends along a central axis 57 that is oriented along the longitudinal direction L. Thus, the central axis 57 can extend along a straight linear direction. The central axis 57 can further define a central axis of the fusion cage 20. The central axis 57 can divide the fusion cage 20 between the first side 23 and the second side 25. Otherwise stated, the first and second sides 23 and 25 are on opposite sides of the central axis 57 with respect to the lateral direction A.

The actuator shaft 50 can be coupled to each of the first and second wedge members 44 and 46. For instance, the actuator shaft 50 has a first or proximal section 52, and a second or distal section 54 opposite the first section 52 and aligned with the first section 52 along the longitudinal direction L. The first and second sections 52 and 54 can be monolithic with each other, and part of the same single unitary structure that defines the actuator 48. At least a portion up to an entirety of the first section 52 can include at least one external thread that defines a first or proximal threaded portion 53 that extends along at least a portion up to an entirety of the first section 52. Similarly, at least a portion up to an entirety of the second section 54 can include at least one external thread that defines a second or distal threaded portion 55 that extends along at least a portion up to an entirety of the second section 54. The actuator 48 can formed from a biocompatible polymeric material or metallic alloy, such as a titanium or steel. In one example, the intervertebral fusion cage 20 includes the single actuator 48 having the single actuator shaft 50, such that the actuator 48 defines the only actuator shaft 50 of the fusion cage 20 that is coupled to wedge members.

As will be described in more detail below, the first threaded portion 53 can be threadedly mated with the first wedge member 44, and the second threaded portion 55 can be threadedly mated with the second wedge member 46. Thus, rotation of the actuator 48, and thus of the actuator shaft 50, causes the first and second wedge members 44 and 46 to translate along the same single actuator shaft 50, for instance along the first and second sections 52 and 54, respectively. In particular, the first wedge member 44 translates along the first threaded portion 53, and the second wedge member 46 translates along the second threaded portion 55. In one example, the translation of the first and second wedge members 44 and 46 along the actuator shaft 50 can be a pure translation, meaning that the first and second wedge members 44 and 46 do not rotate about the central axis 57 of the actuator shaft 50 with respect to the upper and lower endplate members 36 and 38 as they translate along the actuator shaft 50.

The first threaded portion 53 can have a first thread pattern, and the second threaded portion 55 can have a second thread pattern that is opposite the thread first threaded portion 53. For instance, the first threaded portion 53 can have a right-hand thread pattern, and the second threaded portion 55 can have a left-hand thread pattern. Accordingly, rotation of the actuator shaft 50 in a first direction of rotation causes the wedge members 44 and 46 to move toward each other in the expansion direction. Rotation of the actuator shaft 50 in a second direction of rotation opposite the first direction of rotation causes the wedge members 44 and 46 to move away from each other in the contraction direction. Further, the first threaded portion 53 and the second threaded portion 55 can define equal and opposite thread pitches, such that the wedge members 44 and 46 move at the same rate along the actuator shaft 50 in both the expansion direction and in the contraction direction. Alternatively, the first threaded portion 53 and the second threaded portion 55 can define unequal and opposite thread pitches, such that one of the first and second wedge members 44 and 46 moves at a first rate along the actuator shaft 50, and the other of the first and second wedge members 44 and 46 moves at a second rate different than the first rate along the actuator shaft 50. Thus, respective proximal and distal ends of the cage body 21 can be expanded at different rates, thereby imparting a wedge shape to the cage body 21 in the medial-lateral direction when the fusion cage 20 is in the expanded position. While rotation of the actuator 48 causes the wedge members 44 and 46 to selectively move in the expansion direction and the contraction in one example, it is appreciated in other examples that the actuator 48 can be alternatively constructed as desired, such that any suitable movement of the actuator 48 causes the wedge members 44 and 46 to selectively move in the expansion direction and contraction direction.

In one example, the first and second wedge members 44 and 46 move toward each other in the expansion direction, and move away from each other in the contraction direction. It is recognized in other embodiments that the upper and lower endplate members 36 and 38 and the first and second wedge members 44 and 46 can be configured such that the first and second wedge members 44 and 46 move away from each other in the expansion direction, and toward each other in the contraction direction.

The actuator 48 can further include a locating flange 56 that projects radially out from the actuator shaft 50. The locating flange 56 can engage one of the upper and lower endplate members 36 and 38 so as to prevent or limit movement of the actuator 48 relative to the endplate members 36 and 38 along the longitudinal direction L during use, while permitting rotation of the actuator 48 relative to the endplate members 36 and 38. In one example, the actuator 48 includes a slot 58 that extends into the locating flange 56 and is configured to receive a complementary projection 60 of the lower endplate member 38 to prevent movement of the actuator 48 along the longitudinal direction L. Alternatively, the actuator 48 can include a projection that is received in a slot of the lower endplate member 38 both when the fusion cage 20 is in the contracted position and when the fusion cage 20 is in the expanded position.

The fusion cage 20 can further include at least one stop member 62 that is configured to limit expansion of the fusion cage 20, thereby preventing overexpansion of the fusion cage. For instance, the at least one stop member 62 can include a first or proximal stop member 62 a and a second or distal stop member 62 b. The stop members 62 a-b can be configured as sleeves that can be disposed about the first and second sections 52 and 54, respectively, of the actuator shaft 50. The stop members 62 a-b can be unthreaded or otherwise not threadedly coupled to the actuator shaft 50. The first stop member 62 a can be disposed between the locating flange 56 and the first wedge member 44, and the second stop member 62 b can be disposed between the locating flange 56 and the second wedge member 46. As will be described in more detail below, the first and second stop members 62 a and 62 b can abut the locating flange 56 and the first and second wedge members 44 and 46, respectively, when the fusion cage 20 is moved from the contracted position to the expanded position so as to prevent further expansion of the fusion cage 20.

The lower endplate member 38 will now be described with reference to FIGS. 2 and FIGS. 3A-3B. The lower endplate member 38 can include a lower plate portion 64 having an outer surface 65 that defines the lower bone contacting surface 30, and an inner surface 67 opposite the outer surface 65. The lower endplate member 38 can further include at least one bone graft aperture that extends through the lower plate portion 64 from the lower bone contacting surface 30 to the inner surface 67. The bone graft aperture is configured to receive bone graft material to enhance fusion of the lower endplate member 38 with the inferior vertebral body 26. The lower endplate member 38 can include recesses 69 that are configured to receive at least a portion of the actuator 48 when the fusion cage 20 is in the contracted position.

The lower endplate member 38 can include a cradle 66 that extends from the inner surface 67. The cradle 66 includes first and second opposed cradle side walls 68 and 70, respectively that are spaced from each other along the lateral direction A and sized to receive and engage the locating flange 56 of the actuator 48. The cradle 66 can further include at least one projection 60 extends from either or both of the first and second cradle walls 68 and 70 toward the other of the first and second cradle walls 68 and 70. The projection 60 is sized to be inserted in the slot 58 of the locating flange 56 when the cradle is inserted into the cradle 66. Accordingly, the cradle 66 of the lower endplate member 38 can interlock with the actuator 48 to limit or prevent the actuator 48 from translating along the longitudinal direction L with respect to the lower endplate member 38. The actuator 48 is rotatable in the cradle about the central axis 57 in the manner described above. The cradle 66 can be substantially U-shaped or alternatively shaped as desired. The at least one projection 60 can be configured as a single projection that extends along each of the first and second cradle walls 68 and 70. Alternatively, the at least one projection 60 can include a first projection that extends along the first cradle wall 68 and a second projection separate from the first projection that extends along the second cradle wall 70.

In one example, the first cradle wall 68 can define a concave surface that faces the second cradle wall 70, and the second cradle wall can define a convex surface that faces the first cradle wall 68. The projection 60 at the first cradle wall 68 can extend along the concave surface, and thus can similarly be concave. Similarly, the projection 60 at the second cradle wall 70 can extend along the convex surface, and can thus similarly be convex. Thus, the cradle 66 can define a central cradle axis that extends along a curved path in the first lateral direction from the second side 25 of the fusion cage 20 toward the first side 23 of the fusion cage 20 as it extends upward or superiorly. In one example, the curved path can be an arcuate path. As illustrated in FIGS. 10A-10B, the lordotic expansion of the fusion cage 20 can cause the actuator 48 to travel along the curved path as the fusion cage moves between the contracted position to the expanded position.

With continuing reference to FIG. 2 and FIGS. 3A-3B, and as described above, the lower endplate member 38 can include at least one first lower ramp surface 41 and the at least one second lower ramp surface 43, which can each be opposite the lower bone contacting surface 30 along the transverse direction T. For instance, the at least one first lower ramp surface 41 and the at least one second lower ramp surface 43 can be mirror images of each other. The at least one first lower ramp surface 41 can include first and second ramp surfaces 72 and 74, respectively, and the at least one second lower ramp surface 43 can include third and fourth ramp surfaces 76 and 78, respectively. The first and second ramp surfaces 72 and 74 can be referred to as first and second lower proximal ramp surfaces, respectively, of the lower endplate member 38. The third and fourth ramp surfaces 76 and 78 can be referred to as first and second lower distal ramp surfaces, respectively, of the lower endplate member 38.

The first ramp surface 72 of the lower endplate member 38 can be disposed at the first side 23 of the fusion cage 20, and the second ramp surface 74 can be disposed at the second side 25 of the fusion cage 20. The first and second ramp surfaces 72 and 74 of the lower endplate member 38 can be spaced from each other and opposite each other along the lateral direction A. The third ramp surface 76 of the lower endplate member 38 can be disposed at the first side 23 of the fusion cage, and the fourth ramp surface 78 can disposed at the second side 25 of the fusion cage. The third and fourth ramp surfaces 76 and 78 of the lower endplate member 38 can be spaced from each other and opposite each other along the lateral direction A. The first ramp surface 72 and the third ramp surface 76 can be aligned with each other along the longitudinal direction L, and the second ramp surface 74 and the fourth ramp surface 78 can be aligned with each other along the longitudinal direction L. In this regard, the first ramp surface 72 and the third ramp surface 76 can be mirror images of each other. Similarly, the second ramp surface 74 and the fourth ramp surface 78 can be mirror images of each other.

As described above, the fusion cage 20 can be configured to undergo lordotic expansion. Thus, the first and third ramp surfaces 72 and 76 can define a first ramp angle with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A), and the second and fourth ramp surfaces 74 and 78 can define a second ramp angle with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A) that is greater than the first ramp angle. As will be appreciated from the description below, the first, second, third, and fourth ramp surfaces 72-78 of the lower endplate member can be in surface contact with the proximal and distal wedge members 44 and 46, respectively, as the wedge members urge the lower endplate member 38 away from the upper endplate member 36. Further, the first, second, third and fourth ramp surfaces 72-78 are included in the same unitary singular lower endplate member 38, and can be constructed so as to not rotate with respect to each other during movement of the cage body 21 from the contracted position toward the expanded position. Thus, the first, second, third and fourth ramp surfaces 72-78 can be said to be rotatably fixed with respect to each other. Thus, the first ramp angle can be referred to as a fixed first ramp angle, and the second ramp angle can be referred to as a second fixed ramp angle.

Advantageously, the first and second wedge members 44 and 46, respectively, can be configured to maintain surface contact with each of the ramp surfaces 72-78 of the lower endplate member 38 as the fusion cage 20 iterates between the contracted position and the expanded position. Accordingly, each of the first and second ramp surfaces 72 and 74 of the lower endplate member 38 and the third and fourth ramp surfaces 76 and 78 of the lower endplate member 38 can extend along respective nonplanar paths. In one example, the first and second ramp surfaces 72 and 74 of the lower endplate member 38 and the third and fourth ramp surfaces 76 and 78 of the lower endplate member 38 can extend along respective twisted paths. For instance, the first and second ramp surfaces 72 and 74 of the lower endplate member 38 can extend along respective helical paths. The helical paths of the first and second ramp surfaces 72 and 74 can be defined by a common helical pitch, but defined by different helical radii. For instance, the helical paths of the first and second ramp surfaces 72 and 74 can be defined by a single swept helix. Similarly, the third and fourth ramp surfaces 76 and 78 of the lower endplate member 38 can extend along respective helical paths. The helical paths of the third and fourth ramp surfaces 76 and 78 can be defined by the same helical pitch, but defined by different helical radii. For instance, the helical paths of the third and fourth ramp surfaces 76 and 78 can be defined by a single swept helix. The helical paths can be concave in one example.

In one example, the first and second ramp surfaces 72 and 74 extend along a first single lower helical path that is continuous from the first ramp surface 72 to the second ramp surface 74. Similarly, the third and fourth ramp surfaces 76 and 78 can extend along a second single lower helical path that is continuous from the third ramp surface 76 to the fourth ramp surface 78. The first and second lower helical paths can be equal and opposite each other. In this regard, the first and second ramp surfaces 72 and 74 can be mirror images of the third and fourth ramp surfaces 76 and 78 with respect to a plane that is oriented along the lateral direction A and the transverse direction T.

Referring also to FIGS. 8A and 9A, the first ramp surface 72 of the lower endplate member 38 can define a first helical lead-in angle α₁ that can be in a range from approximately 50 degrees to approximately 70 degrees, such as approximately 60 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the helical lead-in angle can define a first ramp angle θ₁ in a range from approximately 20 degrees to approximately 40 degrees, such as approximately 30 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The first ramp angle can be geometrically complementary to the first helical lead-in angle. The third ramp surface 76 of the lower endplate member 38 can also define the first helical lead-in angle α₁ that can be in the range from approximately 50 degrees to approximately 70 degrees, such as approximately 60 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the first helical lead-in angle of the third ramp surface 76 can define the first ramp angle θ₁ in a range from approximately 20 degrees to approximately 40 degrees, such as approximately 30 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The first ramp angle θ₁ can be geometrically complementary to the first helical lead-in angle α₁. The first ramp angle θ₁ of the third ramp surface 76 can be oriented opposite the first ramp angle θ₁ of the first ramp surface 72.

The second ramp surface 74 of the lower endplate member 38 can define a second helical lead-in angle α₂ that can be in a range from approximately 26 degrees to approximately 48 degrees, such as approximately 35 degrees with respect to a respective plane that includes the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the second helical lead-in angle can define a second ramp angle θ₂ in a range from approximately 42 degrees to approximately 64 degrees, such as approximately 55 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The second ramp angle θ₂ can be geometrically complementary to the second helical lead-in angle α₂. The fourth ramp surface 78 of the lower endplate member 38 can also define the second helical lead-in angle α₂ that can be in the range from approximately 26 degrees to approximately 48 degrees, such as approximately 35 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the second helical lead-in angle of the fourth ramp surface 78 can define the second ramp angle θ₂ in the range from approximately 40 degrees to approximately 65 degrees, such as approximately 55 degrees, with respect to the longitudinal direction L (or the plane that includes the longitudinal direction L and the lateral direction A). The second ramp angle θ₂ can be geometrically complementary to the second helical lead-in angle α₂. The second ramp angle θ₂ of the fourth ramp surface 78 can be oriented opposite the second ramp angle θ₂ of the second ramp surface 74.

Referring again to FIGS. 2 and 3A-3B, while the first and second ramp surfaces 72 and 74 are separate ramp surfaces separated from each other along the lateral direction A in one example, it is recognized that the first and second ramp surfaces 72 and 74 can alternatively be continuous with each other so as to define a single ramp surface as desired. Similarly, while the third and fourth ramp surfaces 76 and 78 are separate ramp surfaces separated from each other along the lateral direction A in one example, it is recognized that the third and fourth ramp surfaces 76 and 78 can alternatively be continuous with each other so as to define a single ramp surface as desired.

The lower endplate member 38 can be interlinked with the first and second wedge members 44 and 46. In one example, the lower endplate member 38 can include an interlinking member that is configured to engage complementary interlinking members of the first and second wedge members 44 and 46, respectively. For instance, the interlinking member of the lower endplate member 38 can include first or proximal slots 71 disposed adjacent the first and second ramp surfaces 72 and 74, and second or distal slots 73 that are disposed adjacent the third and fourth ramp surfaces 76 and 78. The first and second slots 71 and 73 can be configured to receive the complementary interlinking members of the first and second wedge members 44 and 46, respectively. It is recognized, of course, that the interlinking member of the lower endplate member 38 can alternatively define projections that is received in a recesses of the first and second wedge members 44 and 46, respectively.

The upper endplate member 36 will now be described with reference to FIGS. 2 and FIGS. 4A-4B. The upper endplate member 36 can include an upper plate portion 80 having an outer surface 81 that defines the upper bone contacting surface 28, and an inner surface 83 opposite the outer surface 81. The inner surfaces 67 and 83 of the lower and upper endplates 36 and 38, respectively, can face each other along the transverse direction T. The upper endplate member 36 can further include at least one bone graft aperture 93 that extends through the upper plate portion 80 from the upper bone contacting surface 28 to the inner surface 83. The bone graft aperture 93 is configured to receive bone graft material to enhance fusion of the upper endplate member 34 with the superior vertebral body 24. The upper endplate member 36 can include recesses 82 that are configured to receive at least a portion of the actuator 48 when the fusion cage 20 is in the contracted position.

As described above, the upper endplate member 36 can include at least one first or proximal upper ramp surface 37 and the at least one second or distal upper ramp surface 39, which can each be opposite the upper bone contacting surface 28 along the longitudinal direction L. For instance, the at least one first or proximal upper ramp surface 37 and the at least one second or distal upper ramp surface 39 can be mirror images of each other. The at least one first upper ramp surface 37 can include first and second ramp surfaces 86 and 88, respectively, and the at least one second lower ramp surface 39 can include third and fourth ramp surfaces 90 and 92, respectively. The first and second ramp surfaces 86 and 88 can be referred to as first and second upper proximal ramp surfaces, respectively, of the upper endplate member 36. The third and fourth ramp surfaces 90 and 92 can be referred to as first and second upper distal ramp surfaces, respectively, of the upper endplate member 36.

The first ramp surface 86 of the upper endplate member 36 can be disposed at the first side 23 of the fusion cage 20, and the second ramp surface 88 can be disposed at the second side 25 of the fusion cage 20. The first and second ramp surfaces 86 and 88 of the upper endplate member 36 can be spaced from each other and opposite each other along the lateral direction A. The third ramp surface 90 of the upper endplate member 36 can be disposed at the first side 23 of the fusion cage, and the fourth ramp surface 92 can disposed at the second side 25 of the fusion cage. The third and fourth ramp surfaces 90 and 92 of the upper endplate member 36 can be spaced from each other and opposite each other along the lateral direction A. The first ramp surface 86 and the third ramp surface 90 can be aligned with each other along the longitudinal direction L, and the second ramp surface 88 and the fourth ramp surface 92 can be aligned with each other along the longitudinal direction L.

As described above, the fusion cage 20 can be configured to undergo lordotic expansion. Thus, the first and third ramp surfaces 86 and 90 can define the first ramp angle with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A), and the second and fourth ramp surfaces 88 and 92 can define a second ramp angle with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A) that is greater than the first ramp angle. The first ramp angle defined by the first and third ramp surfaces 86 and 90 can be substantially equal and opposite the first ramp angle of the first and third ramp surfaces 72 and 76 of the lower endplate member 38. The second ramp angle defined by the second and fourth ramp surfaces 88 and 92 can be substantially equal and opposite the second ramp angle of the second and fourth ramp surfaces 74 and 78 of the lower endplate member 38. As will be appreciated from the description below, the first, second, third, and fourth ramp surfaces 86-92 of the upper endplate member 36 can be in surface contact with the proximal and distal wedge members 44 and 46, respectively, as the wedge members urge the upper endplate member 36 away from the lower endplate member 38. Further, the first, second, third and fourth ramp surfaces 86-92 are included in the same unitary singular upper endplate member 36, and can be constructed so as to not rotate with respect to each other during movement of the cage body 21 from the contracted position toward the expanded position. Thus, the first, second, third and fourth ramp surfaces 86-92 can be said to be rotatably fixed with respect to each other. Thus, the first and second ramp angles can be referred to as fixed ramp angles, respectively.

Advantageously, the first and second wedge members 44 and 46, respectively, can be configured to maintain surface contact with each of the ramp surfaces 86-82 of the upper endplate member 36 as the fusion cage 20 iterates between the contracted position and the expanded position. Accordingly, each of the first and second ramp surfaces 86 and 88 of the upper endplate member 36 and the third and fourth ramp surfaces 90 and 92 of the upper endplate member 36 can extend along respective nonplanar paths. In one example, the first and second ramp surfaces 86 and 88 of the upper endplate member 36 and the third and fourth ramp surfaces 90 and 92 of the upper endplate member 36 can extend along respective twisted paths. For instance, the first and second ramp surfaces 86 and 88 of the upper endplate member 36 can extend along respective helical paths. The helical paths of the first and second ramp surfaces 86 and 88 can be defined by a common helical pitch, but defined by different helical radii. For instance, the helical paths of the first and second ramp surfaces 86 and 88 can be defined by a single swept helix. Similarly, the third and fourth ramp surfaces 90 and 92 of the upper endplate member 36 can extend along respective helical paths. The helical paths of the third and fourth ramp surfaces 90 and 92 can be defined by a common helical pitch, but defined by different helical radii. For instance, the helical paths of the third and fourth ramp surfaces 90 and 92 can be defined by a single swept helix. The first and second upper helical paths can be concave in one example.

In one example, the first and second ramp surfaces 86 and 88 extend along a respective first single upper helical path that is continuous from the first ramp surface 86 to the second ramp surface 88. Similarly, the third and fourth ramp surfaces 90 and 92 can extend along a second single upper helical path that is continuous from the third ramp surface 90 to the fourth ramp surface 92. The first and second upper helical paths can be equal and opposite each other. In this regard, the first and second ramp surfaces 86 and 88 can be mirror images of the third and fourth ramp surfaces 90 and 92 with respect to a plane that is oriented along the lateral direction A and the transverse direction T. Further, the first single upper helical path can be a mirror image of the first single lower helical path of the lower endplate member 38. Similarly, the second single upper helical path can be a mirror image of the second single lower helical path of the lower endplate member 38.

Referring also to FIGS. 8A and 9A, the first ramp surface 86 of the upper endplate member 36 can define the first helical lead-in angle α₁ that can be in the range from approximately 50 degrees to approximately 70 degrees, such as approximately 60 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the first helical lead-in angle α₁ of the first ramp surface 86 can define the first ramp angle θ₁ in a range from approximately 20 degrees to approximately 40 degrees, such as approximately 30 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The first ramp angle θ₁ of the first ramp surface 86 can be geometrically complementary to the first helical lead-in angle α₁ of the first ramp surface 86. The third ramp surface 90 of the upper endplate member 36 can also define the first helical lead-in angle α₁ that can be in the range from approximately 50 degrees to approximately 70 degrees, such as approximately 60 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the first helical lead-in angle α₁ of the third ramp surface 90 can define the first ramp angle θ₁ in the range from approximately 20 degrees to approximately 40 degrees, such as approximately 30 degrees, with respect to the longitudinal direction L (or the plane that includes the longitudinal direction L and the lateral direction A). The first ramp angle θ₁ of the third ramp surface 90 can be geometrically complementary to the first helical lead-in angle α₁ of the third ramp surface 90. The first ramp angle θ₁ of the third ramp surface 90 can be oriented opposite the first ramp angle θ₁ of the first ramp surface 86. Further, the first ramp angle θ₁ of the first ramp surface 86 can be oriented opposite the first ramp angle θ₁ of the first ramp surface 72 of the lower endplate member 38 (see FIG. 9A). Further still, the first ramp surface 86 can be oriented parallel with the third ramp surface 76 of the lower endplate member 38 (see FIG. 9A).

The second ramp surface 88 of the upper endplate member 36 can define the second helical lead-in angle α₂ that can be in a range from approximately 26 degrees to approximately 48 degrees, such as approximately 35 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the second helical lead-in angle α₂ of the second ramp surface 88 can define a second ramp angle θ₂ in a range from approximately 42 degrees to approximately 64 degrees, such as approximately 55 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The second ramp angle θ₂ of the second ramp surface 88 can be geometrically complementary to the second helical lead-in angle α₂ of the second ramp surface 88. The fourth ramp surface 92 of the upper endplate member 36 can also define the second helical lead-in angle α₂ that can be in the range from approximately 26 degrees to approximately 48 degrees, such as approximately 35 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the second helical lead-in angle α₂ of the fourth ramp surface 92 can define the second ramp angle θ₂ in the range from approximately 42 degrees to approximately 64 degrees, such as approximately 55 degrees, with respect to the longitudinal direction L (or the plane that includes the longitudinal direction L and the lateral direction A). The second ramp angle θ₂ of the fourth ramp surface 92 can be geometrically complementary to the second helical lead-in angle α₂ of the fourth ramp surface 92. The second ramp angle θ₂ of the fourth ramp surface 92 can be oriented opposite the second ramp angle θ₂ of the second ramp surface 88. Further, the second ramp angle θ₂ of the second ramp surface 88 can be oriented opposite the second ramp angle of the second ramp surface 74 of the lower endplate member 38 (see FIG. 8A). Further still, the second ramp surface 88 can be oriented substantially parallel with the fourth ramp surface 78 of the lower endplate member 38 (see FIG. 8A).

Referring again to FIGS. 2 and 4A-4B, while the first and second ramp surfaces 86 and 88 are separate ramp surfaces separated from each other along the lateral direction A in one example, it is recognized that the first and second ramp surfaces 86 and 88 can alternatively be continuous with each other so as to define a single ramp surface as desired. Similarly, while the third and fourth ramp surfaces 90 and 92 are separate ramp surfaces separated from each other along the lateral direction A in one example, it is recognized that the third and fourth ramp surfaces 90 and 92 can alternatively be continuous with each other so as to define a single ramp surface as desired.

The upper endplate member 36 can be interlinked with the first and second wedge members 44 and 46. In one example, the upper endplate member 36 can include an interlinking member that is configured to engage complementary interlinking members of the first and second wedge members 44 and 46, respectively. For instance, the interlinking member of the upper endplate member 36 can include first or proximal slots 85 disposed adjacent the first and second ramp surfaces 86 and 88, and second or distal slots 87 that are disposed adjacent the third and fourth ramp surfaces 90 and 92. The first and second slots 85 and 87 can be configured to receive the complementary interlinking members of the first and second wedge members 44 and 46, respectively. It is recognized, of course, that the interlinking member of the upper endplate member 36 can alternatively define projections that is received in a recesses of the first and second wedge members 44 and 46, respectively.

Referring now to FIGS. 2-4B, the upper and lower endplate members 36 and 38 can include respective alignment members that engage each other and guide movement of the fusion cage 20 between the contracted position and the expanded position, thereby enhancing the stability and structural integrity of the fusion cage 20. For instance, the lower endplate member 38 can include first and second lower side walls 94 and 96 that extend, for instance up, from the lower plate portion 64. The first and second side walls 94 and 96 are spaced from each other and opposite each other along the lateral direction A. In particular, the first side wall 94 can be disposed at the first side 23 of the fusion cage 20, and the second side wall 96 can be disposed at the second side 25 of the fusion cage 20. The alignment member of the lower endplate member 38 can be supported by the first and second side walls 94 and 96.

For instance, the alignment member of the lower endplate member 38 can include a first at least one lower rib 98 that extends out from an outer surface of the first side wall 94 along a direction away from the central axis 57, and a second at least one lower rib 100 that extends out from an outer surface of the second side wall 96 along a direction away from the central axis 57. The outer surface of the first side wall 94, and thus the first at least one lower rib 98, can define a curvature, such as concave curvature, as it extends along the transverse direction T. The outer surface of the second side wall 96, and thus the second at least one lower rib 100, can define a curvature, such as a convex curvature, as it extends along the transverse direction T.

Similarly, the upper endplate member 36 can include first and second upper side walls 102 and 104 that extend, for instance down, from the upper plate portion 80. The first and second side walls 102 and 104 are spaced from each other and opposite each other along the lateral direction A. In particular, the first side wall 102 can be disposed at the first side 23 of the fusion cage 20, and the second side wall 104 can be disposed at the second side 25 of the fusion cage 20. The alignment member of the upper endplate member 36 can be supported by the first and second side walls 102 and 104.

For instance, the alignment member of the upper endplate member 36 can include a first at least one upper rib 106 that extends out from an inner surface of the first side wall 102 along a direction toward from the central axis 57, and a second at least one upper rib 108 that extends out from an inner surface of the second side wall 104 along a direction toward from the central axis 57. The inner surface of the first side wall 102, and thus the first at least one upper rib 106, can have a curvature, such as a convex curvature, as it extends along the transverse direction T. The inner surface of the second side wall 104, and thus the second at least one upper rib 108, can have a curvature, such as concave curvature, as it extends along the transverse direction T.

In one example, each of the at least one lower ribs and the at least one upper ribs can include a plurality of ribs and slots therebetween, such that the ribs can engage each other in the respective slots when engaged in a sliding relationship that allows for expansion and contraction of the fusion cage 20. For instance, the first at least one lower rib 98 can engage the first at least one upper rib 106, and in particular can be disposed in a slot defined between a pair of adjacent first upper ribs 106. Conversely, the first at least one upper rib 106 can engage the first at least one lower rib 98, and in particular can be disposed in a slot defined between a pair of adjacent first lower ribs 98. Similarly, the second at least one lower rib 100 can engage the second at least one upper rib 108, and in particular can be disposed in a slot defined between a pair of adjacent second upper ribs 108. Conversely, the second at least one upper rib 108 can engage the second at least one lower rib 100, and in particular can be disposed in a slot defined between a pair of adjacent second lower ribs 100. The curvatures of the side walls of the upper and lower endplate members 36 and 38 and corresponding ribs allows the alignment members to remain engaged with each other during expansion of the fusion cage 20, during which the second side 25 of the fusion cage 20 expands at a greater rate than the first side 23 of the fusion cage 20. Thus, the alignment members of the upper and lower endplates 36 and 38 can guide relative movement of the upper and lower endplate members 36 and 38 as the fusion cage 20 iterates between the contracted position and the expanded position. The engagement of the ribs can prevent the first and second endplate members 36 and 38 from translating along the lateral and longitudinal directions during expansion or contraction of the fusion cage 20.

The lower ribs 98 and 100 and the upper ribs 106 and 108 can define any suitable shape as desired. For instance, in one example, the lower ribs 98 and 100 and the upper ribs 106 and 108 can be rectangular in cross section along a plane that is defined by the longitudinal direction L and the lateral direction A. Alternatively, the lower ribs 98 and 100 and the upper ribs 106 and 108 can define interlocking dovetail shapes.

The first and second wedge members 44 and 46 will now be described with reference to FIGS. 2 and 5A-6C. In particular, with initial reference to FIGS. 2 and FIGS. 5A-5C, the first or proximal wedge member 44 defines a first wedge body 110. The first wedge member 44 defines a first bore 111 that extends at least into or through the first wedge body 110 along the longitudinal direction L. The first wedge member 44 can define a first ferrule that extends from the first wedge body 110 in the distal direction, and can define a distalmost surface of the first wedge member 44. The bore 111 can extend proximally through the first ferrule to the proximal surface of the first wedge body 110, which can also define a proximal-most surface of the first wedge member 44.

At least a portion of the bore 111 can be internally threaded and thus configured to threadedly mate with the first threaded portion 53 of the first section 52 of the actuator shaft 50, and thus of the actuator 48. Accordingly, rotation of the actuator 48 in the first direction of rotation causes the first wedge member 44 to translate along the actuator shaft 50, and thus the actuator 48, distally toward the second wedge member 46 in the expansion direction. Rotation of the actuator 48 in the second direction of rotation causes the first wedge member 44 to translate along the actuator shaft 50, and thus the actuator 48, proximally away from the second wedge member 46 in the contraction direction.

The bore 111 can extend through the first wedge body 110, such that the bore 111 is open to the proximal surface of the first wedge member 44. Accordingly, an instrument can access a proximal end 59 (see FIG. 11A) of the actuator 48 through the bore 111, or the actuator 48 can extend proximally through the bore 111. The proximal end 59 of the actuator 48 can include any internal or external geometry that is configured to be engaged by the instrument, such that the instrument and the actuator 48 are rotatably coupled to each other. As a result, rotation of the instrument in the first direction of rotation causes the actuator 48 to correspondingly rotate relative to the cage body 21 in the first direction of rotation. Similarly, rotation of the instrument in the second direction of rotation causes the actuator 48 to rotate relative to the cage body 21 in the second direction of rotation.

It is further recognized that imparting a rotational force to the actuator 48 can similarly impart a rotational force to the cage body 21. As a result, the cage body 21 can include at least one anti-rotation member 120 that is configured to engage an instrument to prevent rotation of the cage body 21 during rotation of the actuator 48. In one example, the anti-rotation member 120 can be configured as anti-rotation apertures 121 that extend distally into the proximal surface of the first wedge member 44. The anti-rotation apertures 121 can be disposed on respective opposite sides of the bore 111. During use, an instrument can include projections that extend into the anti-rotation apertures 121 to prevent rotation of the cage body 21 during rotation of the actuator 48. In one example, the anti-rotation apertures 121 can also be configured to receive bone graft material. In this regard, the anti-rotation apertures 121 can define bone graft channels. Thus, after the fusion cage 20 has reached the expanded position, bone graft injected through the bone graft channels can travel to the interior of the cage body 21, and through the bone graft apertures of the upper and lower endplates 36 and 38 (see FIG. 2 ) to enhance fusion of the bone cage 20 with the superior and inferior vertebral bodies. It should be appreciated that the bone graft channels can be alternatively positioned as desired.

With continuing reference to FIGS. 2 and 5A-5C, and as described above, the first wedge body 110 defines the at least one upper ramp surface 45 and at least one lower ramp surface 47 opposite the at least one upper ramp surface 45 along the transverse direction T. The at least one upper ramp surface 45 can be sloped inferiorly toward the lower bone contacting surface 30 as it extends along the distal direction toward the second wedge member 46. The at least one lower ramp surface 47 can be sloped superiorly toward the upper bone contacting surface 30 as it extends along the distal direction toward the second wedge member 46.

The at least one lower ramp surface 47 of the first or proximal wedge member 44 can include first and second ramp surfaces 112 and 114. The at least one upper ramp surface 45 of the first or proximal wedge member 44 can include third and fourth ramp surfaces 116 and 118, respectively. The first and second ramp surfaces 112 and 114 can be referred to as first and second lower proximal ramp surfaces, respectively, of the first wedge member 44. The third and fourth ramp surfaces 116 and 118 can be referred to as first and second upper proximal ramp surfaces, respectively, of the first wedge member 44.

The first ramp surface 112 of the first wedge member 44 can be disposed at the first side 23 of the fusion cage 20, and the second ramp surface 114 can be disposed at the second side 25 of the fusion cage 20. The first and second ramp surfaces 112 and 114 of the first wedge member 44 can be spaced from each other and opposite each other along the lateral direction A. The third ramp surface 116 of the first wedge member 44 can be disposed at the first side 23 of the fusion cage, and the fourth ramp surface 118 can disposed at the second side 25 of the fusion cage. The third and fourth ramp surfaces 116 and 118 of the first wedge member 44 can be spaced from each other and opposite each other along the lateral direction A. The first ramp surface 112 and the third ramp surface 116 can be aligned with each other along the transverse direction T, and the second ramp surface 114 and the fourth ramp surface 118 can be aligned with each other along the transverse direction T.

As described above, the fusion cage 20 can be configured to undergo lordotic expansion. Thus, the first and third ramp surfaces 112 and 116 can define the first ramp angle with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A), and the second and fourth ramp surfaces 114 and 118 can define the second ramp angle with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A) that is greater than the first ramp angle.

It should thus be appreciated that the first ramp surface 112 of the first wedge member 44 is sloped substantially equal to the first ramp surface 72 of the lower endplate member 38. Further, the second ramp surface 114 of the first wedge member 44 is sloped substantially equal to the second ramp surface 74 of the lower endplate member 38. Similarly, the third ramp surface 116 of the first wedge member 44 is sloped substantially equal to the first ramp surface 86 of the upper endplate member 36. Further, the fourth ramp surface 118 of the first wedge member 44 is sloped substantially equal to the second ramp surface 88 of the upper endplate member 36.

As described above, the fusion cage 20 can undergo lordotic expansion as it iterates from the contracted position to the expanded position. Advantageously, the first ramp surface 112 of the first wedge member 44 can maintain surface contact with the first ramp surface 72 of the lower endplate member 38 as the fusion cage 20 iterates between the contracted position and the expanded position. Further, the second ramp surface 114 of the first wedge member 44 can maintain surface contact with the second ramp surface 74 of the lower endplate member 38 as the fusion cage 20 iterates between the contracted position and the expanded position. Similarly, the third ramp surface 116 of the first wedge member 44 can maintain surface contact with the first ramp surface 86 of the upper endplate member 36 as the fusion cage 20 iterates between the contracted position and the expanded position. Further, the fourth ramp surface 118 of the first wedge member 44 can maintain surface contact with the second ramp surface 88 of the upper endplate member 36 as the fusion cage 20 iterates between the contracted position and the expanded position. The first, second, third and fourth ramp surfaces 112-118 are included in the same unitary singular first wedge member 44, and can be constructed so as to not rotate with respect to each other during movement of the first wedge member 44 in the expansion direction. Thus, the first, second, third and fourth ramp surfaces 112-118 can be said to be rotatably fixed with respect to each other. The first and second ramp angles can therefore be referred to as fixed ramp angles, respectively.

In this regard, the first and second ramp surfaces 112 and 114 of the first wedge member 44 can extend along respective helical wedge paths of the first wedge member 44. The helical wedge paths of the first and second ramp surfaces 112 and 114 of the first wedge member can be defined by a common helical pitch, but defined by different helical radii. For instance, the helical wedge paths of the first and second ramp surfaces 112 and 114 can be defined by a single swept helix. The helical wedge paths of the first and second ramp surfaces 112 and 114 can be complementary to the common respective helical paths of the first and second ramp surfaces 72 and 74 of the lower endplate member 38. Thus, the helical wedge paths of the first and second ramp surfaces 112 and 114 of the first wedge member 44 can define convex helical paths. As a result, the first and second ramp surfaces 112 and 114 of the first wedge member 44 can maintain surface contact with the respective first and second ramp surfaces 72 and 74 of the lower endplate member 38 as the fusion cage 20 iterates between the contracted position and the expanded position. In one example, the first and second ramp surfaces 112 and 114 of the first wedge member 44 can maintain surface contact with the respective first and second ramp surfaces 72 and 74 of the lower endplate member 38 throughout the entire range of motion between the contracted position and the expanded position.

Similarly, the third and fourth ramp surfaces 116 and 118 of the first wedge member 44 can extend along respective helical wedge paths of the first wedge member 44. The helical wedge paths of the third and fourth ramp surfaces 116 and 118 of the first wedge member 44 can be defined by a common helical pitch, but defined by different helical radii. For instance, the helical wedge paths of the third and fourth ramp surfaces 116 and 118 can be defined by a single swept helix. The helical wedge paths of the third and fourth ramp surfaces 116 and 118 can be complementary to the respective helical paths of the first and second ramp surfaces 86 and 88 of the upper endplate member 36. Thus, the helical wedge path of the third and fourth ramp surfaces 116 and 118 of the first wedge member 44 can define respective convex helical paths. As a result, the third and fourth ramp surfaces 116 and 118 of the first wedge member 44 can maintain surface contact with the respective first and second ramp surfaces 86 and 88 of the upper endplate member 36 as the fusion cage 20 iterates between the contracted position and the expanded position. In one example, the third and fourth ramp surfaces 116 and 118 of the first wedge member 44 can maintain surface contact with the respective first and second ramp surfaces 86 and 88, respectively, of the upper endplate member 36 throughout the entire range of motion between the contracted position and the expanded position.

Referring also to FIGS. 8A and 9A, the first ramp surface 112 of the first wedge member 44 can define the first helical lead-in angle α₁ that can be in the range from approximately 50 degrees to approximately 70 degrees, such as approximately 60 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the first helical lead-in angle α₁ of the first ramp surface 112 can define the first ramp angle θ₁ in a range from approximately 20 degrees to approximately 40 degrees, such as approximately 30 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The first ramp angle θ₁ of the first ramp surface 112 can be geometrically complementary to the first helical lead-in angle α₁ of the first ramp surface 112. The third ramp surface 116 of the first wedge member 44 can also define the first helical lead-in angle α₁ that can be in the range from approximately 50 degrees to approximately 70 degrees, such as approximately 60 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the first helical lead-in angle α₁ of the third ramp surface 116 can define the first ramp angle θ₁ in the range from approximately 20 degrees to approximately 40 degrees, such as approximately 30 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The first ramp angle θ₁ of the third ramp surface 116 can be geometrically complementary to the first helical lead-in angle α₁ of the third ramp surface 116. The first ramp angle θ₁ of the third ramp surface 116 can be oriented opposite the first ramp angle θ₁ of the first ramp surface 112 (see FIG. 9A). Further, the first ramp surface 112 can be oriented parallel with the first ramp surface 72 of the lower endplate member 38 (see FIG. 9A).

The second ramp surface 114 of the first wedge member 44 can define the second helical lead-in angle α₂ that can be in a range from approximately 26 degrees to approximately 48 degrees, such as approximately 35 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the second helical lead-in angle α₂ of the second ramp surface 114 can define a second ramp angle θ₂ in a range from approximately 42 degrees to approximately 64 degrees, such as approximately 55 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The second ramp angle θ₂ of the second ramp surface 114 can be geometrically complementary to the second helical lead-in angle α₂ of the second ramp surface 114. The fourth ramp surface 118 of the first wedge member 44 can also define the second helical lead-in angle α₂ that can be in the range from approximately 26 degrees to approximately 48 degrees, such as approximately 35 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the second helical lead-in angle α₂ of the fourth ramp surface 118 can define the second ramp angle θ₂ in the range from approximately 42 degrees to approximately 64 degrees, such as approximately 55 degrees, with respect to the longitudinal direction L (or the plane that includes the longitudinal direction L and the lateral direction A). The second ramp angle θ₂ of the fourth ramp surface 118 can be geometrically complementary to the second helical lead-in angle α₂ of the fourth ramp surface 118. The second ramp angle θ₂ of the fourth ramp surface 118 can be oriented opposite the second helical lead-in angle α₂ of the second ramp surface 114 Further, the fourth ramp surface 118 can be oriented parallel with the second ramp surface 88 of the upper endplate member 36 (see FIG. 8A). Further still, the second ramp angle θ₂ of the fourth ramp surface 118 can be oriented opposite the second ramp angle θ₂ of the fourth ramp surface 92 of the upper endplate member 36 (see FIG. 8A).

As described above, the first wedge member 44 can be interlinked with each of the upper and lower endplate members 36 and 38. Referring again to FIGS. 2 and 5A-5C, the first wedge member 44 can include at least one protrusion that is captured by the upper endplate member 36, and at least one protrusion that is captured by the lower endplate member 38. In particular, the first wedge member 44 can include a first protrusion 122 that extends out from the first wedge body 110 along the lateral direction A. The first protrusion 122 can be spaced below the first ramp surface 112, and aligned with at least a portion of the first ramp surface 112 along the transverse direction T, such that the first wedge member 44 defines a first gap that extends between the first protrusion 122 and the first ramp surface 112. The first wedge member 44 can further include a second protrusion 124 that extends out from the first wedge body 110 along the lateral direction A. The second protrusion 124 can extend out from the first wedge body 110 a direction opposite the first protrusion 122. The second protrusion 124 can be spaced below the second ramp surface 114, and aligned with at least a portion of the second ramp surface 114 along the transverse direction T, such that the first wedge member 44 defines a second gap that extends between the second protrusion 124 and the second ramp surface 114. The first and second protrusions 122 and 124 can be referred to as lower protrusions of the first wedge member 44, or a lower pair of protrusions of the first wedge member 44. While the first and second protrusions 122 and 124 are illustrated as protrusions separate from each other along the lateral direction A, it should be appreciated that the first and second protrusions can alternatively be continuous with each other to define a single unitary protrusion.

Similarly, the first wedge member 44 can include a third protrusion 126 that extends out from the first wedge body 110 along the lateral direction A. The third protrusion 126 can be spaced above the third ramp surface 116, and aligned with at least a portion of the third ramp surface 116 along the transverse direction T, such that the first wedge member 44 defines a third gap that extends between the third protrusion 126 and the third ramp surface 116. The first wedge member 44 can include a fourth protrusion 128 that extends out from the first wedge body 110 along the lateral direction A. The fourth protrusion 128 can be spaced above the fourth ramp surface 118, and aligned with at least a portion of the fourth ramp surface 118 along the transverse direction T, such that the first wedge member 44 defines a fourth gap that extends between the fourth protrusion 128 and the fourth ramp surface 118. The third and fourth protrusions 126 and 128 can be referred to as upper protrusions of the first wedge member 44, or an upper pair of protrusions of the first wedge member 44. While the third and fourth protrusions 126 and 128 are illustrated as protrusions separate from each other along the lateral direction A, it should be appreciated that the third and fourth protrusions 126 and 128 can alternatively be continuous with each other to define a single unitary protrusion.

The first wedge member 44 can interlink with the upper and lower endplates 36 and 38, respectively. In particular, the first and second protrusions 122 and 124 can be disposed in respective ones of the first slots 71 of the lower endplate member 38 (see FIGS. 3A-3B). Similarly, the third and fourth protrusions 126 and 128 can be disposed in respective ones of the first slots 85 of the upper endplate member 36 (see FIGS. 4A-4B). Accordingly, the first wedge member 44 can be captured by each of the upper and lower endplate members 36 and 38. Further, as the first wedge member 44 is moved in the contraction direction, the first and second protrusions 122 and 124 can ride along respective ramped inner surfaces of the lower endplate member 38 opposite the first and second ramp surfaces 72 and 74 (see FIGS. 3A-3B), which can urge the lower endplate member 38 toward the upper endplate member 36 along the transverse direction T. Similarly, as the first wedge member 44 is moved in the contraction direction, the third and fourth protrusions 126 and 128 can ride along respective ramped inner surfaces of the upper endplate member 36 opposite the first and second ramp surfaces 86 and 88 (see FIGS. 4A-4B), which can urge the upper endplate member 36 toward the lower endplate member 38 along the transverse direction T. Thus, both the height and lordotic curvature of the cage 20 can be reduced. Alternatively or additionally, movement of the first wedge member 44 in the contraction direction allows anatomical or other forces to cause the upper and lower endplate members 36 and 38 to move toward each other.

The second or distal wedge member 46 will now be described with reference to FIG. 2 and FIGS. 6A-6C. In particular, the second wedge member 46 defines a second wedge body 130. The second wedge member 46 defines a second bore 113 that extends at least into or through the second wedge body 130 along the longitudinal direction L. The second wedge member 46 can define a second ferrule that extends from the second wedge body 130 in the proximal direction, and can define a proximal-most surface of the second wedge member 46. The bore 113 can extend distally through the second ferrule toward or to a distal surface of the second wedge body 130 that can also define the distal surface of the second wedge member 46. The bore 113 can extends through the second ferrule.

At least a portion of the bore 113 can be internally threaded and thus configured to threadedly mate with the second threaded portion 55 of the second section 54 of the actuator shaft 50, and thus of the actuator 48. Accordingly, rotation of the actuator 48 in the first direction of rotation causes the second wedge member 46 to translate along the actuator shaft 50, and thus the actuator 48, proximally toward the first wedge member 44 in the expansion direction. Rotation of the actuator 48 in the second direction of rotation causes the second wedge member 46 to translate along the actuator shaft 50, and thus the actuator 48, proximally away from the first wedge member 44 in the contraction direction. While the first and second wedge members 44 and 46 can be threadedly coupled to the actuator 48, it is recognized that they wedge members 44 and 46 can be coupled to the actuator 48 in accordance with any suitable alternative embodiment that can allow or cause the wedge members 44 and 46 to move in the expansion direction, and in some examples also selectively in the contraction direction.

The second wedge body 130, and thus the second wedge member 46, defines the at least one upper ramp surface 49 and the at least one lower ramp surface 51 opposite the at least one upper ramp surface 49 along the transverse direction T. The at least one upper ramp surface 49 can be sloped inferiorly toward the lower bone contacting surface 30 as it extends in the proximal direction toward the first wedge member 44. The at least one lower ramp surface 51 can be sloped superiorly toward the upper bone contacting surface 28 as it extends in the proximal direction toward the first wedge member 44.

The at least one lower ramp surface 51 of the second or distal wedge member 46 can include first and second ramp surfaces 132 and 134. The at least one upper ramp surface 49 of the second or distal wedge member 46 can include third and fourth ramp surfaces 136 and 138, respectively. The first and second ramp surfaces 132 and 134 can be referred to as first and second lower proximal ramp surfaces, respectively, of the second wedge member 46. The third and fourth ramp surfaces 136 and 138 can be referred to as first and second upper proximal ramp surfaces, respectively, of the second wedge member 46.

The first ramp surface 132 of the second wedge member 46 can be disposed at the first side 23 of the fusion cage 20, and the second ramp surface 134 can be disposed at the second side 25 of the fusion cage 20. The first and second ramp surfaces 132 and 134 of the second wedge member 46 can be spaced from each other and opposite each other along the lateral direction A. The third ramp surface 136 of the second wedge member 46 can be disposed at the first side 23 of the fusion cage, and the fourth ramp surface 138 can disposed at the second side 25 of the fusion cage. The third and fourth ramp surfaces 136 and 138 of the second wedge member 46 can be spaced from each other and opposite each other along the lateral direction A. The first ramp surface 132 and the third ramp surface 136 can be aligned with each other along the transverse direction T, and the second ramp surface 134 and the fourth ramp surface 138 can be aligned with each other along the transverse direction T.

As described above, the fusion cage 20 can be configured to undergo lordotic expansion. Thus, the first and third ramp surfaces 132 and 136 can define the first ramp angle with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A), and the second and fourth ramp surfaces 134 and 138 can define the second ramp angle with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A) that is greater than the first ramp angle.

It should thus be appreciated that the first ramp surface 132 of the second wedge member 46 is sloped substantially equal to the third ramp surface 76 of the lower endplate member 38. Further, the second ramp surface 134 of the second wedge member 46 is sloped substantially equal to the fourth ramp surface 78 of the lower endplate member 38. Similarly, the third ramp surface 136 of the second wedge member 46 is sloped substantially equal to the third ramp surface 90 of the upper endplate member 36. Further, the fourth ramp surface 138 of the second wedge member 46 is sloped substantially equal to the fourth ramp surface 92 of the upper endplate member 36.

As described above, the fusion cage 20 can undergo lordotic expansion as it iterates from the contracted position to the expanded position. Advantageously, the first ramp surface 132 of the second wedge member 46 can maintain surface contact with the third ramp surface 76 of the lower endplate member 38 as the fusion cage 20 iterates between the contracted position and the expanded position. Further, the second ramp surface 134 of the second wedge member 46 can maintain surface contact with the fourth ramp surface 78 of the lower endplate member 38 as the fusion cage 20 iterates between the contracted position and the expanded position. Similarly, the third ramp surface 136 of the second wedge member 46 can maintain surface contact with the third ramp surface 90 of the upper endplate member 36 as the fusion cage 20 iterates between the contracted position and the expanded position. Further, the fourth ramp surface 138 of the second wedge member 46 can maintain surface contact with the fourth ramp surface 92 of the upper endplate member 36 as the fusion cage 20 iterates between the contracted position and the expanded position. The first, second, third and fourth ramp surfaces 132-138 are included in the same unitary singular second wedge member 46, and can be constructed so as to not rotate with respect to each other during movement of the second wedge member 46 in the expansion direction. Thus, the first, second, third and fourth ramp surfaces 132-138 can be said to be rotatably fixed with respect to each other. The first and second ramp angles can therefore be referred to as fixed ramp angles, respectively.

In this regard, the first and second ramp surfaces 132 and 134 of the second wedge member 46 can extend along respective helical wedge paths of the second wedge member 46. The helical wedge paths of the first and second ramp surfaces 132 and 134 of the second wedge member 46 can be defined by a common helical pitch, but defined by different helical radii. For instance, the helical wedge paths of the first and second ramp surfaces 132 and 134 can be defined by a single swept helix. The helical wedge paths of the first and second ramp surfaces 132 and 134 of the second wedge member 46 can be complementary to the helical paths of the third and fourth ramp surfaces 76 and 78 of the lower endplate member 38. Thus, the helical wedge paths of the first and second ramp surfaces 132 and 134 of the second wedge member 46 can therefore define a convex helical path that is complementary to the concave helical paths of the third and fourth ramp surfaces 76 and 78 of the lower endplate member 38. As a result, the first and second ramp surfaces 132 and 134 of the first wedge member 44 can maintain surface contact with the respective third and fourth ramp surfaces 76 and 78 of the lower endplate member 38 as the fusion cage 20 iterates between the contracted position and the expanded position. In one example, the first and second ramp surfaces 132 and 134 of the first wedge member 44 can maintain surface contact with the respective third and fourth ramp surfaces 76 and 78 of the lower endplate member 38 throughout the entire range of motion between the contracted position and the expanded position.

Similarly, the third and fourth ramp surfaces 136 and 138 of the second wedge member 46 can extend along respective upper helical wedge paths of the second wedge member 46. The helical wedge paths of the third and fourth ramp surfaces 136 and 138 of the second wedge member 46 can be defined by a common helical pitch, but defined by different helical radii. For instance, the helical wedge paths of the third and fourth ramp surfaces 136 and 138 can be defined by a single swept helix. The upper helical wedge paths can be complementary to the respective helical paths of the third and fourth ramp surfaces 90 and 92 of the upper endplate member 36. Thus, the respective helical wedge paths of the third and fourth ramp surfaces 136 and 138 of the second wedge member 46 can define a convex helical path. As a result, the third and fourth ramp surfaces 136 and 138 of the second wedge member 46 can maintain surface contact with the respective third and fourth ramp surfaces 90 and 92 of the upper endplate member 36 as the fusion cage 20 iterates between the contracted position and the expanded position. In one example, the third and fourth ramp surfaces 136 and 138 of the second wedge member 46 can maintain surface contact with the respective third and fourth ramp surfaces 90 and 92 of the upper endplate member 36 throughout the entire range of motion between the contracted position and the expanded position.

Referring also to FIGS. 8A and 9A, the first ramp surface 132 of the second wedge member 46 can define the first helical lead-in angle α₁ that can be in the range from approximately 50 degrees to approximately 70 degrees, such as approximately 60 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the first helical lead-in angle α₁ of the first ramp surface 132 can define the first ramp angle θ₁ in a range from approximately 20 degrees to approximately 40 degrees, such as approximately 30 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The first ramp angle θ₁ of the first ramp surface 132 can be geometrically complementary to the first helical lead-in angle α₁ of the first ramp surface 132. The third ramp surface 136 of the second wedge member 46 can also define the first helical lead-in angle α₁ that can be in the range from approximately 50 degrees to approximately 70 degrees, such as approximately 60 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the first helical lead-in angle α₁ of the third ramp surface 136 can define the first ramp angle θ₁ in the range from approximately 20 degrees to approximately 40 degrees, such as approximately 30 degrees, with respect to the longitudinal direction L (or the plane that includes the longitudinal direction L and the lateral direction A). The first ramp angle θ₁ of the third ramp surface 136 can be geometrically complementary to the first helical lead-in angle α₁ of the third ramp surface 136. The first ramp angle θ₁ of the third ramp surface 136 can be oriented opposite the first ramp angle θ₁ of the first ramp surface 132. Further, the first ramp angle θ₁ of the first ramp surface 132 can be oriented parallel with the first ramp angle of the third ramp surface 116 of the first wedge member 44 (see FIG. 9A). Further still, the first ramp angle θ₁ of the first ramp surface 132 can be oriented opposite the first ramp angle θ₁ of the first ramp surface 112 of the first wedge member 44 (see FIG. 9A).

The second ramp surface 134 of the second wedge member 46 can define the second helical lead-in angle α₂ that can be in a range from approximately 26 degrees to approximately 48 degrees, such as approximately 35 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the second helical lead-in angle α₂ of the second ramp surface 134 can define a second ramp angle θ₂ in a range from approximately 42 degrees to approximately 64 degrees, such as approximately 55 degrees, with respect to the longitudinal direction L (or a plane that includes the longitudinal direction L and the lateral direction A). The second ramp angle θ₂ of the second ramp surface 134 can be geometrically complementary to the second helical lead-in angle α₂ of the second ramp surface 134. The fourth ramp surface 138 of the second wedge member 46 can also define the second helical lead-in angle α₂ that can be in the range from approximately 26 degrees to approximately 48 degrees, such as approximately 35 degrees with respect to the transverse direction T (or a respective plane that includes the transverse direction T and the lateral direction A). Thus, the second helical lead-in angle α₂ of the fourth ramp surface 138 can define the second ramp angle θ₂ in the range from approximately 42 degrees to approximately 64 degrees, such as approximately 55 degrees, with respect to the longitudinal direction L (or the plane that includes the longitudinal direction L and the lateral direction A). The second ramp angle θ₂ of the fourth ramp surface 138 can be geometrically complementary to the second helical lead-in angle α₂ of the fourth ramp surface 138. The second ramp angle θ₂ of the fourth ramp surface 138 can be oriented opposite the second ramp angle θ₂ of the second ramp surface 134. Further, the fourth ramp surface 138 can be oriented parallel with the fourth ramp surface 92 of the upper endplate member 36 (see FIG. 8A). Further still, the second ramp angle θ₂ of the fourth ramp surface 138 can be oriented opposite the second ramp angle θ₂ of the fourth ramp surface 118 of the first wedge member 44 (see FIG. 8A).

As described above, the second wedge member 46 can be interlinked with each of the upper and lower endplate members 36 and 38. That is, the second wedge member 46 can include at least one protrusion that is captured by the upper endplate member 36, and at least one protrusion that is captured by the lower endplate member 38. In particular, the second wedge member 46 can include a first protrusion 140 that extends out from the second wedge body 130 along the lateral direction A. The first protrusion 140 can be spaced below the first ramp surface 132, and aligned with at least a portion of the first ramp surface 132 along the transverse direction T, such that the second wedge member 46 defines a first gap that extends between the first protrusion 140 and the first ramp surface 132. The second wedge member 46 can further include a second protrusion 142 that extends out from the second wedge body 130 along the lateral direction A. The second protrusion 142 can extend out from the second wedge body 130 a direction opposite the first protrusion 140. The second protrusion 142 can be spaced below the second ramp surface 134, and aligned with at least a portion of the second ramp surface 134 along the transverse direction T, such that the second wedge member 46 defines a second gap that extends between the second protrusion 142 and the second ramp surface 134. The first and second protrusions 140 and 142 can be referred to as lower protrusions of second wedge member 46, or a lower pair of protrusions of the second wedge member 46. While the first and second protrusions 140 and 142 are illustrated as protrusions separate from each other along the lateral direction A, it should be appreciated that the first and second protrusions 140 and 142 can alternatively be continuous with each other to define a single unitary protrusion.

Similarly, the second wedge member 46 can include a third protrusion 144 that extends out from the second wedge body 130 along the lateral direction A. The third protrusion 144 can be spaced above the third ramp surface 136, and aligned with at least a portion of the third ramp surface 136 along the transverse direction T, such that the second wedge member 46 defines a third gap that extends between the third protrusion 144 and the third ramp surface 136. The second wedge member 46 can include a fourth protrusion 146 that extends out from the second wedge body 130 along the lateral direction A. The fourth protrusion 146 can be spaced above the fourth ramp surface 138, and aligned with at least a portion of the fourth ramp surface 138 along the transverse direction T, such that the second wedge member 46 defines a fourth gap that extends between the fourth protrusion 146 and the fourth ramp surface 138. The third and fourth protrusions 144 and 146 can be referred to as upper protrusions of the second wedge member 46, or an upper pair of protrusions of the second wedge member 46. While the third and fourth protrusions 144 and 146 are illustrated as protrusions separate from each other along the lateral direction A, it should be appreciated that the third and fourth protrusions 144 and 146 can alternatively be continuous with each other to define a single unitary protrusion.

The second wedge member 46 can interlink with the upper and lower endplates 36 and 38, respectively. In particular, the first and second protrusions 140 and 142 can be disposed in respective ones of the second slots 73 of the lower endplate member 38 (see FIGS. 3A-3B). Similarly, the third and fourth protrusions 144 and 146 can be disposed in respective ones of the second slots 87 of the upper endplate member 36 (see FIGS. 4A-4B). Accordingly, the second wedge member 46 can be captured by each of the upper and lower endplate members 36 and 38. Further, as the second wedge member 46 is moved in the contraction direction, the first and second protrusions 140 and 142 can ride along respective ramped inner surfaces of the lower endplate member 38 opposite the third and fourth ramp surfaces 76 and 78 (see FIGS. 3A-3B), which can urge the lower endplate member 38 toward the upper endplate member 36 along the transverse direction T. Similarly, as the second wedge member 46 is moved in the contraction direction, the third and fourth protrusions 144 and 146 can ride along respective ramped inner surfaces of the upper endplate member 36 opposite the third and fourth ramp surfaces 90 and 92 (see FIGS. 4A-4B), which can urge the upper endplate member 36 toward the lower endplate member 38 along the transverse direction T. Thus, both the height and lordotic curvature of the cage 20 can be reduced. Alternatively or additionally, movement of the second wedge member 46 in the contraction direction allows anatomical or other forces to cause the upper and lower endplate members 36 and 38 to move toward each other.

Operation of the fusion cage 20 will now be described with initial reference to FIGS. 7A-9B. In particular, when the fusion cage 20 is in the contracted position, the upper and lower bone contacting surfaces 28 and 30 can be substantially parallel to each other. In particular, the upper and lower bone contacting surfaces 28 and 30 can each substantially extend along respective planes that are oriented along the longitudinal direction L and the lateral direction A. In other examples, the upper and lower bone contacting surfaces 28 and 30 can be angled with respect to each other when the fusion cage 20 is in the contracted position. For instance, the upper and lower bone contacting surfaces 28 and 30 can be lordotically angled with respect to each other when the fusion cage 20 is in the contracted position The angle defined by the upper and lower bone contacting surfaces 28 and 30 can become increasingly lordotic during expansion of the implant to the expanded position as described herein. Further, when the fusion cage 20 is in the contracted position, first and second sides 23 and 25 of the fusion cage 20 define a first or contracted height H1 along the transverse direction T that extends from the upper bone contacting surface 28 to the lower bone contacting surface 30. Further, in one example the upper and lower endplate members 36 and 38 abut each other such that the implant 20 is unable to achieve a height less than the first height H1 due to movement of the wedge members 44 and 46 in the contraction direction. In particular, the inner surface 67 of the lower plate portion 64 of the lower endplate member 38 and the inner surface 83 of the upper plate portion 80 of the upper plate member 36 can abut each other. Accordingly, fusion cage 20 can be configured such that the actuator shaft 48 is unable to be rotated in the second direction of rotation when the cage is in the contracted position.

When it is desirable to expand the fusion cage 20, the actuator 48 is rotated in the first direction of rotation relative to the cage body 21. The first direction of rotation can be clockwise. Alternatively, the first direction of rotation can be counterclockwise. Rotation of the actuator 48 in the first direction of rotation, causes the first and second wedge members 44 and 46 to travel in the expansion direction. In one example, the first and second wedge members 44 and 46 can travel along the actuator shaft 50 toward each other in the expansion direction.

As described above, the first and third ramp surfaces 112 and 116 of the first wedge member 44 abut the first ramp surface 72 of the lower endplate member 38 and the first ramp surface 86 of the upper endplate member 36, respectively. The first and third ramp surfaces 112 and 116 can be referred to as a first pair 148 a of wedge ramp surfaces at the first side 23 of the cage body 21. The first ramp surface 72 of the lower endplate member 38 and the first ramp surface 86 of the upper endplate member 36 can be referred to as a first pair 148 b of endplate ramp surfaces at the first side 23 of the cage body 21. During movement of the first wedge member 44 in the expansion direction, the first ramp surface 112 rides along the first ramp surface 72 of the lower endplate member, and urges the first ramp surface 72 away from the upper endplate member 36. Further, the third ramp surface 116 rides along the first ramp surface 86 of the upper endplate member 36, and urges the first ramp surface 86 away from the lower endplate member 38.

The second and fourth ramp surfaces 114 and 118 of the first wedge member 44 abut the second ramp surface 74 of the lower endplate member 38 and the second ramp surface 88 of the upper endplate member 36, respectively. The second and fourth ramp surfaces 114 and 118 can be referred to as a second pair 150 a of wedge ramp surfaces at the second side 25 of the cage body 21. The second ramp surface 74 of the lower endplate member 38 and the second ramp surface 88 of the upper endplate member 36 can be referred to as a second pair 150 b of endplate ramp surfaces. During movement of the first wedge member 44 in the expansion direction, the second ramp surface 114 rides along the second ramp surface 74 of the lower endplate member 38, and urges the second ramp surface 74 away from the upper endplate member 36. Further, the fourth ramp surface 118 rides along the second ramp surface 88 of the upper endplate member 36, and urges the second ramp surface 88 away from the lower endplate member 38.

The first and third ramp surfaces 132 and 136 of the second wedge member 46 abut the third ramp surface 76 of the lower endplate member 38 and the third ramp surface 90 of the upper endplate member 36, respectively. The first and third ramp surfaces 132 and 136 can be referred to as a third pair 152 a of wedge ramp surfaces at the first side 23 of the cage body 21. The third ramp surface 76 of the lower endplate member 38 and the third ramp surface 90 of the upper endplate member 36 can be referred to as a third pair 152 b of endplate ramp surfaces at the first side 23 of the cage body 21. During movement of the second wedge member 46 in the expansion direction, the first ramp surface 132 rides along the third ramp surface 76 of the lower endplate member 38, and urges the third ramp surface 76 away from the upper endplate member 36. Further, the third ramp surface 136 rides along the third ramp surface 90 of the upper endplate member 36, and urges the third ramp surface 90 away from the lower endplate member 38.

The second and fourth ramp surfaces 134 and 138 of the second wedge member 46 abut the fourth ramp surface 78 of the lower endplate member 38 and the fourth ramp surface 92 of the upper endplate member 36, respectively. The second and fourth ramp surfaces 134 and 138 can be referred to as a fourth pair 154 a of wedge ramp surfaces at the second side 25 of the cage body 21. The fourth ramp surface 78 of the lower endplate member 38 and the fourth ramp surface 92 of the upper endplate member 36 can be referred to as a fourth pair 154 b of endplate ramp surfaces at the second side 23 of the cage body 21. During movement of the second wedge member 46 in the expansion direction, the second ramp surface 134 rides along the fourth ramp surface 78 of the lower endplate member 38, and urges the fourth ramp surface 78 away from the upper endplate member 36. Further, the fourth ramp surface 138 rides along the fourth ramp surface 92 of the upper endplate member 36, and urges the fourth ramp surface 92 away from the lower endplate member 38.

As described above, the first and third pairs 148 a-b and 152 a-b of wedge ramp surfaces and endplate ramp surfaces at the first side 23 of the cage body 21 can define respective first ramp angles with respect to the longitudinal direction L. The second and fourth pairs 150 a-b and 154 a-b of wedge ramp surfaces and endplate ramp surfaces at the second side 25 of the cage body 21 define respective second ramp angles with respect to the longitudinal direction. The second ramp angles can be greater than the first ramp angles. As the first and second wedge members 44 and 46 move in the expansion direction, respective entireties of the first and second endplate members 36 and 38 move away from each other along the transverse direction.

It is recognized of course, that in certain surgical applications, the lower endplate member 38 can be supported, for instance by the inferior vertebral surface 42 of the inferior vertebral body 26 (see FIG. 1 ). Accordingly, when the endplate is expanded from the contracted position to the expanded position, the lower endplate member 38 can remain supported by the inferior vertebral surface, such that upper endplate member 36 moves away from the lower endplate member 38 while the lower endplate member 38 remains substantially stationary with respect to expansion along the transverse direction T. However, as this is due to the particular surgical application, it can nevertheless be said that the upper and lower endplate members 36 and 38 are movable away from each other along the transverse direction T, and angulate with respect to each other as described above. In other embodiments, the wedge members 44 and 46 can include only their upper ramp surfaces and not include lower ramp surfaces, such that the wedge members 44 and 46 urge the upper endplate member 36 away from the lower endplate member 38 without urging the lower endplate member 38 away from the upper endplate member 36 as the fusion cage 20 moves to the lordotic expanded position.

Further, the first and second endplate members 36 and 38 move away from each other along the transverse direction at a greater rate at second side 25 of the cage body 21 than at the first side 23 of the cage body 21. As a result, when the fusion cage 20 is in the expanded position, the fusion cage 20 can be wedge-shaped along a direction from the second side 25 of the cage body 21 toward the first side 23 of the cage body 21 along the lateral direction A. In particular, the fusion cage 20 has a second height H2 at the first side 23 of the cage body 21 that extends from the upper bone contacting surface 28 to the lower bone contacting surface 30 along the transverse direction T. The fusion cage 20 has a third height H3 at the second side 25 of the cage body 21 that extends from the upper bone contacting surface 28 to the lower bone contacting surface 30 along the transverse direction T. The second height H2 that is defined when the fusion cage 20 is in the expanded position is greater than the first height H1 that is defined when the fusion cage 20 is in the contracted position. The third height H3 that is defined when the fusion cage is in the expanded position is greater than the second height H2. Thus, the upper and lower bone contacting surfaces 28 and 30 define an angle with respect to each other in a plane that is defined by the lateral direction A and the transverse direction T. The angle can be defined in the first lateral direction from the second side 25 of the fusion cage 20 toward the first side 23. The angle can be in a range from approximately 3 degrees to approximately 20 degrees, for instance from approximately 5 degrees to approximately 10 degrees. It is appreciated that the angle can increase as the cage expands from the contracted position to the expanded position.

Advantageously, the first and second wedge members 44 and 46, respectively, can be configured to maintain surface contact with each of the ramp surfaces 72-78 of the lower endplate member 38 when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position. That is, at least respective majorities up to respective entireties of the first and third ramp surfaces 112 and 116 of the first wedge member 44 can be in contact with the first ramp surface 72 of the lower endplate member 38 and the first ramp surface 86 of the upper endplate member 36, respectively, when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position. Alternatively or additionally, at least respective majorities up to respective entireties of the first ramp surface 72 of the lower endplate member 38 and the first ramp surface 86 of the upper endplate member 36 can be in contact with the first and third ramp surfaces 112 and 116 of the first wedge member 44, respectively, when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position.

Further, at least respective majorities up to respective entireties of the second and fourth ramp surfaces 114 and 118 of the first wedge member 44 can be in contact with the second ramp surface 74 of the lower endplate member 38 and the second ramp surface 88 of the upper endplate member 36, respectively, when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position. Alternatively or additionally, at least respective majorities up to respective entireties of the second ramp surface 74 of the lower endplate member 38 and the second ramp surface 88 of the upper endplate member 36 can be in contact with the second and fourth ramp surfaces 114 and 118 of the first wedge member 44, respectively, when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position.

Similarly, at least respective majorities up to respective entireties of the first and third ramp surfaces 132 and 136 of the second wedge member 46 can be in contact with the third ramp surface 76 of the lower endplate member 38 and the third ramp surface 90 of the upper endplate member 36, respectively, when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position. Alternatively or additionally, at least respective majorities up to respective entireties of the third ramp surface 76 of the lower endplate member 38 and the third ramp surface 90 of the upper endplate member 36, respectively, can be in contact with the first and third ramp surfaces 132 and 136 of the second wedge member 46, respectively, when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position.

Further, at least respective majorities up to respective entireties of the second and fourth ramp surfaces 134 and 138 of the second wedge member 46 can be in contact with the fourth ramp surface 78 of the lower endplate member 38 and the fourth ramp surface 92 of the upper endplate member 36, respectively, when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position. Alternatively or additionally, at least respective majorities up to respective entireties of the fourth ramp surface 78 of the lower endplate member 38 and the fourth ramp surface 92 of the upper endplate member 36 can be in contact with the second and fourth ramp surfaces 134 and 138 of the second wedge member 46, respectively, when the fusion cage 20 is in the compressed position, as the fusion cage 20 iterates between the contracted position and the expanded position, and when the fusion cage 20 is in the expanded position.

The surface contact during lordotic expansion, each of the first, second, third, and fourth pairs 148 a-b, 150 a-b, 152 a-b, and 154 a-b of wedge ramp surfaces and endplate ramp surfaces can define non-planar surfaces that maintain surface contact during lordotic expansion of the fusion cage 20. In some examples, the non-planar surfaces can define curvatures. For instance, the non-planar surfaces can be twisted. For instance, the non-planar surfaces can define helical curvatures. The curvatures of ramp surfaces that abut each other can be complementary to each other. Accordingly, the ramp surfaces that abut each other can nest with each other as they ride along each other. Thus, the ramp surfaces that abut each other can maintain surface contact with each other during at least a portion of the movement of the fusion cage 20 from the contracted position to the expanded position, and from the expanded position to the contracted position. Further, the ramp surfaces that abut each other can maintain surface contact with each other during an entirety of the movement of the fusion cage 20 from the contracted position to the expanded position, and from the expanded position to the contracted position.

Further, the first wedge member 44 and the second wedge member 46 can be substantially symmetrical with respect to each other, meaning that the first and second wedge members 44 and 46 can be symmetrical with respect to each other with the exception of the anti-rotation apertures 121 of the first wedge member 44 in some instances. Thus, it can be said that the first wedge body 110 and the ramp surfaces of the first wedge member 44 can have a size and shape that is substantially symmetrical with respect to the size and shape of the second wedge body 130 and the ramp surfaces of the second wedge member 46. Accordingly, the first ramp surface 112 of the first wedge member 44 can be substantially symmetrical with respect to the first ramp surface 132 of the second wedge member 46. Further, the second ramp surface 114 of the first wedge member 44 can be substantially symmetrical with respect to the second ramp surface 134 of the second wedge member 46. Further, the third ramp surface 116 of the first wedge member 44 can be substantially symmetrical with respect to the third ramp surface 136 of the second wedge member 46. Further still, the fourth ramp surface 118 of the first wedge member 44 can be substantially symmetrical with respect to the fourth ramp surface 138 of the second wedge member 46.

Referring now also to FIGS. 11A-11B, and as described above, the fusion cage 20 can include first and second stop members 62 a-b that can be configured to limit expansion of the fusion cage. In particular, the stop members 62 a-b can be mounted onto the actuator shaft 50, and thus the actuator 48, at a location between respective first and second stop structures that move toward each other in response to movement of the fusion cage 20 from the contracted position to the expanded position. Referring to the first stop member 62 a, the first stop structure can be defined by the first wedge member 44, and the second stop structure can be defined by the locating flange 56 of the actuator 48 or any suitable alternative structure of or supported by the actuator 48. Referring to the second stop member 62 b, the first stop structure can be defined by the second wedge member 46, and the second structure can be defined by the locating flange 56 of the actuator 48 or any suitable alternative stop structure of or supported by the actuator 48. The stop members 62 a-b can be unthreaded and thus freely slidable along the actuator shaft 50. Alternatively, the stop members 62 a-b can be translatably fixed to the locating flange 56 or alternative first structure.

During operation, as the wedge members 44 and 46 move toward each other in the expansion direction, the wedge members 44 and 46 also move toward the locating flange 56. Thus, the first and second wedge members 44 and 46 can move in the expansion direction from the initial position to a stop position whereby the stop members 62 a-63 b are in abutment with both the respective first and second stop structures, which thereby prevents further movement of the wedge members 44 and 46 in the expansion direction, and correspondingly preventing further rotation of the actuator 48 in the first direction of rotation. Because the wedge members 44 and 46 can be positioned at symmetric locations of the actuator shaft 50, it is appreciated that both wedge members 44 and 46 can abut the respective stop members 62 a and 62 b simultaneously when the stop members 62 a and 62 b are in abutment with the respective first stop structure. In other examples, movement of either of the wedge members 44 and 46 in the expansion direction can be prevented due to abutment with the corresponding stop member 62, thereby preventing further rotation of the actuator 48.

It is appreciated that the fusion cage can define the expanded position when the wedge members 44 and 46 are disposed at any position spaced from the initial position in the expansion direction. The fusion cage 20 is configured to maintain the expanded position in response to compressive anatomical forces applied by the inferior vertebral body 26 and the superior vertebral body 24. In one example, frictional forces between the actuator 48 and the wedge members 44 and 46 can prevent the anatomical forces from causing the wedge members 44 and 46 to move in the contraction direction. In this regard, it is recognized that the ramp surfaces of the wedge members 44 and 46 are in abutment with the complementary ramp surfaces of the upper and lower endplates 36 and 38.

Although the disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present disclosure is not intended to be limited to the particular embodiments described in the specification. As one of ordinary skill in the art will readily appreciate from that processes, machines, manufacture, composition of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. 

What is claimed:
 1. An expandable intervertebral fusion cage for insertion in an intervertebral space defined between a superior vertebral body and an inferior vertebral body, the fusion cage comprising: a cage body including: an upper endplate member defining an upper bone contacting surface configured to abut the superior vertebral body, the upper endplate member further including at least one proximal upper ramp surface and at least one distal upper ramp surface that each extend along respective helical paths, wherein the at least one proximal ramp surface of the upper endplate member comprises first and second ramp surfaces of the upper endplate member spaced from each other along a lateral direction, and the at least one distal ramp surface of the upper endplate member comprises third and fourth ramp surfaces of the upper endplate member spaced from each other along the lateral direction; a lower endplate member defining a lower bone contacting surface configured to abut the inferior vertebral body, wherein the upper and lower bone contacting surfaces are opposite each other along a transverse direction; a proximal wedge member having at least one upper ramp surface that abuts the at least one proximal upper ramp surface of the upper endplate member; a distal wedge member having at least one upper ramp surface that abuts the at least one distal upper ramp surface of the upper endplate member, wherein the proximal and distal wedge members are opposite each other along a longitudinal direction that is perpendicular to the transverse direction, wherein the cage body defines a first side and a second side opposite the first side along the lateral direction that is perpendicular to each of the longitudinal direction and the transverse direction; and an actuator having an actuator shaft that defines a proximal section coupled to the proximal wedge member and a distal section that is coupled to the distal wedge member and aligned with the proximal section along the longitudinal direction, such that movement of the actuator in a first direction causes the proximal and distal wedge members to move in an expansion direction whereby (i) the at least one upper ramp surface of the proximal wedge member rides along the at least one proximal upper ramp surface of the upper endplate member in surface contact with the at least one proximal upper ramp surface of the upper endplate member, and (ii) the at least one upper ramp surface of the distal wedge member rides along the at least one distal upper ramp surface of the upper endplate member in surface contact with the at least one distal upper ramp surface of the upper endplate member, thereby causing an entirety of the upper endplate member to move away from the lower endplate member, wherein movement of the proximal and distal wedge members in the expansion direction causes the upper endplate member at the second side of the fusion cage to move away from the lower endplate at a greater rate than the upper endplate member at the first side of the fusion cage moves away from the lower endplate member, thereby causing lordotic expansion of the intervertebral fusion cage.
 2. The expandable intervertebral fusion cage of claim 1, wherein: the lower endplate member further includes at least one proximal lower ramp surface and at least one distal lower upper ramp surface, the proximal wedge member further comprises at least one lower ramp surface, the distal wedge member further comprises at least one lower ramp surface, movement of the proximal and distal wedge members in the expansion direction causes (i) the at least one lower ramp surface of the proximal wedge member to ride along the at least one proximal lower ramp surface of the lower endplate member in surface contact with the at least one proximal lower ramp surface of the lower endplate member, and (ii) the at least one lower ramp surface of the distal wedge member to ride along the at least one distal lower ramp surface of the lower endplate member in surface contact with the at least one distal lower ramp surface of the lower endplate member, thereby causing an entirety of the lower endplate member to move away from the upper endplate member, and wherein movement of the proximal and distal wedge members in the expansion direction causes the lower endplate member at the second side of the fusion cage to move away from the upper endplate at a greater rate than the lower endplate member at the first side of the fusion cage moves away from the upper endplate member.
 3. The expandable intervertebral fusion cage of claim 2, wherein all ramp surfaces of the upper and lower endplate members and proximal and distal wedge members extend along respective non-planar paths.
 4. The expandable intervertebral fusion cage of claim 3, wherein the respective non-planar paths define respective helical paths.
 5. The expandable intervertebral fusion cage of claim 1, wherein the actuator comprises a single actuator shaft having proximal and distal threaded portions that are threadedly coupled to the proximal and distal wedge members, respectively, such that rotation of the actuator in a first direction of rotation causes the proximal and distal wedge members to translate along the actuator shaft in the expansion direction.
 6. The expandable intervertebral fusion cage of claim 1, wherein the proximal and distal wedge members are substantially symmetrical with respect to each other.
 7. The expandable intervertebral fusion cage of claim 1, wherein the proximal and distal wedge members undergo pure translation along the actuator shaft as they move along the expansion direction.
 8. The expandable intervertebral fusion cage of claim 1, wherein the actuator shaft is the only actuator shaft of the intervertebral fusion cage.
 9. The expandable intervertebral fusion cage of claim 1, wherein the upper and lower endplate members have respective ribs at each of the first and second sides of the cage that engage each other so as to guide movement of the upper and lower endplates away from each other, wherein the ribs define a curvature as they extend along the transverse direction.
 10. The expandable intervertebral fusion cage of claim 1, wherein the actuator further comprises a locating flange that extends from the actuator shaft, and the lower endplate member defines a cradle that receives the locating flange so as to limit movement of the actuator shaft relative to the lower endplate member along the longitudinal direction, and the cradle defines a central cradle axis that extends along a lateral curved path in a direction from the second side of the cage toward the first side of the cage as it extends upward.
 11. The expandable intervertebral fusion cage of claim 1, wherein the proximal and distal wedge members comprise respective protrusions that are captured in respective slots of the upper and lower endplate member, so as to interlink the proximal and distal wedge members with the upper and lower endplate members.
 12. The expandable intervertebral fusion cage of claim 1, wherein: the at least one upper ramp surface of the proximal wedge member comprises first and second proximal ramp surfaces opposite each other along the lateral direction, and the at least one lower ramp surface of the proximal wedge member comprises third and fourth proximal ramp surfaces, wherein the first and third proximal ramp surfaces are disposed at the first side of the cage body and define respective first ramp angles that are equal and opposite each with respect to the longitudinal direction, the second and fourth proximal ramp surfaces are disposed at the second side of the cage body and define respective second ramp angles that are equal and opposite each other with respect to the longitudinal direction, the second ramp angles being greater than the first ramp angle.
 13. The expandable intervertebral fusion cage of claim 12, wherein: the at least one upper ramp surface of the distal wedge member comprises first and second distal ramp surfaces opposite each other along the lateral direction, and the at least one lower ramp surface of the distal wedge member comprises third and fourth distal ramp surfaces, wherein the first and third distal ramp surfaces are disposed at the first side of the cage body and are define the respective first ramp angles that are equal and opposite each other with respect to the longitudinal direction, the second and fourth distal ramp surfaces are disposed at the second side of the cage body and define the respective second ramp angles that are equal and opposite each other with respect to the longitudinal direction.
 14. The expandable intervertebral fusion cage of claim 13, wherein: the first ramp surface of the proximal wedge member is sloped equal and opposite the first ramp surface of the distal wedge member, the second ramp surface of the proximal wedge member is sloped equal and opposite the second ramp surface of the distal wedge member, the third ramp surface of the proximal wedge member is sloped equal and opposite the third ramp surface of the distal wedge member, and the fourth ramp surface of the proximal wedge member is sloped equal and opposite the fourth ramp surface of the distal wedge member.
 15. The expandable intervertebral fusion cage of claim 13, wherein: the first, second, third, and fourth ramp surfaces of the proximal wedge member are rotatably fixed with respect to each other, and the first, second, third, and fourth ramp surfaces of the distal wedge member are rotatably fixed with respect to each other.
 16. An expandable intervertebral fusion cage for insertion in an intervertebral space defined between a superior vertebral body and an inferior vertebral body, the fusion cage comprising: a cage body including: an upper endplate member defining an upper bone contacting surface configured to abut the superior vertebral body, the upper endplate member further including at least one proximal upper ramp surface and at least one distal upper ramp surface that each extend along respective helical paths; a lower endplate member defining a lower bone contacting surface configured to abut the inferior vertebral body, wherein the upper and lower bone contacting surfaces are opposite each other along a transverse direction; a proximal wedge member having at least one upper ramp surface that abuts the at least one proximal upper ramp surface of the upper endplate member; a distal wedge member having at least one upper ramp surface that abuts the at least one distal upper ramp surface of the upper endplate member, wherein the proximal and distal wedge members are opposite each other along a longitudinal direction that is perpendicular to the transverse direction, wherein the cage body defines a first side and a second side opposite the first side along a lateral direction that is perpendicular to each of the longitudinal direction and the transverse direction; and an actuator having an actuator shaft that defines a proximal section coupled to the proximal wedge member and a distal section that is coupled to the distal wedge member and aligned with the proximal section along the longitudinal direction, such that movement of the actuator in a first direction causes the proximal and distal wedge members to move in an expansion direction whereby (i) the at least one upper ramp surface of the proximal wedge member rides along the at least one proximal upper ramp surface of the upper endplate member in surface contact with the at least one proximal upper ramp surface of the upper endplate member, and (ii) the at least one upper ramp surface of the distal wedge member rides along the at least one distal upper ramp surface of the upper endplate member in surface contact with the at least one distal upper ramp surface of the upper endplate member, thereby causing an entirety of the upper endplate member to move away from the lower endplate member, wherein the actuator shaft is the only actuator shaft of the intervertebral fusion cage, and wherein movement of the proximal and distal wedge members in the expansion direction causes the upper endplate member at the second side of the fusion cage to move away from the lower endplate at a greater rate than the upper endplate member at the first side of the fusion cage moves away from the lower endplate member, thereby causing lordotic expansion of the intervertebral fusion cage.
 17. The expandable intervertebral fusion cage of claim 16, wherein the upper and lower endplate members have respective ribs at each of the first and second sides of the cage that engage each other so as to guide movement of the upper and lower endplates away from each other, wherein the ribs define a curvature as they extend along the transverse direction.
 18. The expandable intervertebral fusion cage of claim 16, wherein: the at least one upper ramp surface of the proximal wedge member comprises first and second proximal ramp surfaces opposite each other along the lateral direction, and the at least one lower ramp surface of the proximal wedge member comprises third and fourth proximal ramp surfaces, wherein the first and third proximal ramp surfaces are disposed at the first side of the cage body and define respective first ramp angles that are equal and opposite each with respect to the longitudinal direction, the second and fourth proximal ramp surfaces are disposed at the second side of the cage body and define respective second ramp angles that are equal and opposite each other with respect to the longitudinal direction, the second ramp angles being greater than the first ramp angle.
 19. An expandable intervertebral fusion cage for insertion in an intervertebral space defined between a superior vertebral body and an inferior vertebral body, the fusion cage comprising: a cage body including: an upper endplate member defining an upper bone contacting surface configured to abut the superior vertebral body, the upper endplate member further including at least one proximal upper ramp surface and at least one distal upper ramp surface that each extend along respective helical paths; a lower endplate member defining a lower bone contacting surface configured to abut the inferior vertebral body, wherein the upper and lower bone contacting surfaces are opposite each other along a transverse direction; a proximal wedge member having at least one upper ramp surface that abuts the at least one proximal upper ramp surface of the upper endplate member; a distal wedge member having at least one upper ramp surface that abuts the at least one distal upper ramp surface of the upper endplate member, wherein the proximal and distal wedge members are opposite each other along a longitudinal direction that is perpendicular to the transverse direction, wherein the cage body defines a first side and a second side opposite the first side along a lateral direction that is perpendicular to each of the longitudinal direction and the transverse direction; and an actuator having an actuator shaft that defines a proximal section coupled to the proximal wedge member and a distal section that is coupled to the distal wedge member and aligned with the proximal section along the longitudinal direction, such that movement of the actuator in a first direction causes the proximal and distal wedge members to move in an expansion direction whereby (i) the at least one upper ramp surface of the proximal wedge member rides along the at least one proximal upper ramp surface of the upper endplate member in surface contact with the at least one proximal upper ramp surface of the upper endplate member, and (ii) the at least one upper ramp surface of the distal wedge member rides along the at least one distal upper ramp surface of the upper endplate member in surface contact with the at least one distal upper ramp surface of the upper endplate member, thereby causing an entirety of the upper endplate member to move away from the lower endplate member, wherein movement of the proximal and distal wedge members in the expansion direction causes the upper endplate member at the second side of the fusion cage to move away from the lower endplate at a greater rate than the upper endplate member at the first side of the fusion cage moves away from the lower endplate member, thereby causing lordotic expansion of the intervertebral fusion cage, and wherein the upper and lower endplate members have respective ribs at each of the first and second sides of the cage that engage each other so as to guide movement of the upper and lower endplates away from each other, wherein the ribs define a curvature as they extend along the transverse direction.
 20. The expandable intervertebral fusion cage of claim 19, wherein: the at least one upper ramp surface of the proximal wedge member comprises first and second proximal ramp surfaces opposite each other along the lateral direction, and the at least one lower ramp surface of the proximal wedge member comprises third and fourth proximal ramp surfaces, wherein the first and third proximal ramp surfaces are disposed at the first side of the cage body and define respective first ramp angles that are equal and opposite each with respect to the longitudinal direction, the second and fourth proximal ramp surfaces are disposed at the second side of the cage body and define respective second ramp angles that are equal and opposite each other with respect to the longitudinal direction, the second ramp angles being greater than the first ramp angle. 